Major urinary proteins
Encyclopedia
Major urinary proteins (Mups), also known as α2u-globulins, are a subfamily
of proteins found in abundance in the urine
and other secretion
s of many animals. Mups provide a small range of identifying information about the donor animal, when detected by the vomeronasal organ
of the receiving animal. They belong to a larger family
of proteins known as lipocalin
s. Mups are encoded by a cluster of genes
, located adjacent to each other on a single stretch of DNA, that varies greatly in number between species: from at least 21 functional genes in mice to none in humans. Mup proteins form a characteristic glove
shape, encompassing a ligand
-binding pocket that accommodates specific small, organic chemicals.
Urinary proteins were first reported in rodents in 1932, during studies by Thomas Addis
into the cause of proteinuria
. They are potent human allergen
s, and are largely responsible for a number of animal allergies
, including to cats, horses and rodents. Their endogenous
function within an animal is unknown, but may involve regulating energy expenditure. However, as secreted proteins they play multiple roles in chemical communication between animals, functioning as pheromone
transporters and stabilizers in rodents and pigs. Mups can also act as protein pheromones themselves. They have been demonstrated to promote aggression
in male mice, and one specific Mup protein found in male mouse urine is sexually attractive to female mice. Mups can also function as signals between different species
: mice display an instinctive fear response on the detection of Mups derived from predators such as cats and rats.
, the excess of protein in human urine, as an indicator of kidney disease. To better understand the etiology
of proteinuria, some scientists attempted to study the phenomenon in laboratory animals
. Between 1932 and 1933 a number of scientists, including Thomas Addis
, independently reported the surprising finding that some healthy rodents have protein in their urine. However, it was not until the 1960s that the major urinary proteins of mice and rats were first described in detail. It was found that the proteins are primarily made in the liver
of males and secreted through the kidney
s into the urine in large quantities (milligrams per day).
Since they were named, the proteins have been found to be differentially expressed in other glands
that secrete products directly into the external environment. These include lacrimal
, parotid, submaxillary, sublingual
, preputial
and mammary glands. In some species, such as cats and pigs, Mups appear not to be expressed in urine at all and are mainly found in saliva. Sometimes the term urinary Mups (uMups) is used to distinguish those Mups expressed in urine from those in other tissues.
of between 15 and 35 genes and pseudogene
s in the mouse and by an estimated 20 genes in the rat. In 2008 a more precise number of Mup genes in a range of species was determined by analyzing the DNA sequence
of whole genome
s.
has at least 21 distinct Mup genes (with open reading frame
s), and a further 21 Mup pseudogenes (with reading frame
s disrupted by a nonsense mutation
or an incomplete gene duplication
). They are all clustered together, arrayed side by side across 1.92 megabases of DNA on chromosome 4. The 21 functional genes have been divided into two sub-classes based on position and sequence similarity: 6 peripheral Class A Mups, and 15 central Class B Mups. The central Class B Mup gene cluster formed through a number of sequential duplications from one of the Class A Mups. As all the Class B genes are almost identical to each other, researchers have concluded that these duplications occurred very recently in mouse evolution. Indeed, the repetitive structure of these central Mup genes means they are likely to be unstable and may vary in number among wild mice. The Class A Mups are more different from each other and are therefore likely to be more stable, older genes but what, if any, functional differences the classes have are unknown. The similarity between the genes makes the region difficult to study using current DNA sequencing technology
. Consequently the Mup gene cluster is one of the few parts of the mouse whole genome sequence with gaps remaining, and further genes may remain undiscovered.
Rat urine also contains homologous urinary proteins; although they were originally given a different name, α2u-globulins
, they have since become known as rat Mups. Rats have 9 distinct Mup genes and a further 13 pseudogenes clustered together across 1.1 megabases of DNA on chromosome 5. Like in mice, the cluster formed by multiple duplications. However, this occurred independently of the duplications in mice, meaning that both rodent species expanded their Mup gene families separately, but in parallel
.
s have at least two. Insects, fish, amphibia, birds and marsupial
s appear to have disrupted synteny
at the chromosomal position of the Mup gene cluster, suggesting the gene family may be specific to placental mammals. Humans are the only placental mammals found not to have any active Mup genes; instead they have a single Mup pseudogene containing a mutation that causes missplicing
, rendering it dysfunctional.
) proteins known as lipocalin
s. They have a characteristic structure
of eight beta sheet
s arranged in an anti-parallel
beta barrel open on one face, with alpha helices
at both ends. Consequently, they form a characteristic glove shape, encompassing a cup-like pocket
that binds small organic chemicals with high affinity. A number of these ligands bind to mouse Mups, including 2-sec-butyl-4,5-dihydrothiazole
(abbreviated as SBT or DHT), 6-hydroxy-6-methyl-3-heptanone
(HMH) and 2,3 dihydro-exo-brevicomin (DHB). These are all urine-specific chemicals that have been shown to act as pheromones—molecular signals excreted by one individual that trigger an innate behavioural response in another member of the same species. Mouse Mups have also been shown to function as pheromone stabilizers, providing a slow release mechanism that extends the potency of volatile pheromones in male urine scent marks. Given the diversity of Mups in rodents, it was originally thought that different Mups may have differently shaped binding pockets and therefore bind different pheromones. However, detailed studies found that most variable sites
are located on the surface of the proteins, and appear to have little effect on ligand binding.
Rat Mups bind different small chemicals. 1-Chlorodecane
is the most common ligand, with 2-methyl-N-phenyl-2-propenamide
, hexadecane
and 2,6,11-trimethyl decane found to be less prominent. Rat Mups also bind limonene
-1,2-epoxide, resulting in a disease of the host's kidney, hyaline
-droplet nephropathy
, that progresses to cancer. Other species do not develop this disorder because their Mups do not bind that particular chemical. Accordingly, when transgenic mice
were engineered to express the rat Mup their kidneys developed the disease.
The Mup found in pigs, named salivary lipocalin (SAL), is expressed in the salivary gland of males where it tightly binds androstenone
and androstenol
, both pheromones that cause female pigs to assume a mating stance
.
Isothermal titration calorimetry
studies performed with Mups and associated ligands (pyrazines, alcohols, thiazolines, 6-hydroxy-6-methyl-3-heptanone, and N-phenylnapthylamine,) revealed an unusual binding phenomena. The active site
has been found to be suboptimally hydrated, resulting in ligand binding being driven by enthalpic
dispersion forces. This is contrary to most other proteins, which exhibit entropy
-driven binding forces from the reorganisation of water molecules. This unusual process has been termed the "nonclassical hydrophobic effect."
and accelerate the estrus cycle in female mice, inducing the Vandenbergh
and Whitten effect
s. However, in both cases the Mups had to be presented to the female dissolved in male urine, indicating that the protein requires some urinary context to function. In 2007 Mups normally found in male mouse urine were made in transgenic bacteria, and therefore created devoid of the chemicals they normally bind. These Mups were shown to be sufficient to promote aggressive
behaviour in males, even in the absence of urine. In addition, Mups made in bacteria were found to activate olfactory sensory neurons in the vomeronasal organ (VNO), a subsystem of the nose known to detect pheromones via specific sensory receptor
s, of mice and rats. Together, this demonstrated that Mup proteins can act as pheromones themselves, independent of their ligands.
Consistent with a role in male-male aggression, adult male mice secrete significantly more Mups into their urine than females, juveniles or castrated male mice. The precise mechanism driving this difference between the sexes
is complex, but at least three hormones—testosterone
, growth hormone
and thyroxine
—are known to positively influence the production of Mups in mice. Wild house mouse
urine contains variable combinations of four to seven distinct Mup proteins per mouse. Some inbred laboratory mouse strains
, such as BALB/c
and C57BL/6, also have different proteins expressed in their urine. However, unlike wild mice, different individuals from the same strain express the same protein pattern, an artifact of many generations of inbreeding
. One unusual Mup is less variable than the others: it is consistently produced by a high proportion of wild male mice and is almost never found in female urine. When this Mup was made in bacteria and used in behavioural testing, it was found to attract female mice. Other Mups were tested but they did not have the same attractive qualities, suggesting the male-specific Mup acts as a sex pheromone. Scientists named this Mup darcin as a humorous reference to Fitzwilliam Darcy
, the romantic hero from Pride and Prejudice
. Taken together, the complex patterns of Mups produced has the potential to provide a range information about the donor animal, such as gender
, fertility, social dominance
, age, genetic diversity
or kinship
. Wild mice (unlike laboratory mice that are genetically identical and which therefore also have identical patterns of Mups in the urine) have individual patterns of Mup expression in their urine that act as a "barcode
" to uniquely identify the owner of a scent mark.
s—chemical signals that transmit information between species. Mice are instinctively afraid of the smell of their natural predators, including cats and rats. This occurs even in laboratory mice that have been isolated from predators for hundreds of generations. When the chemical cues responsible for the fear
response were purified from cat saliva and rat urine, two homologous protein signals were identified: Fel d 4 (Felis domesticus allergen 4), the product of the cat Mup gene, and Rat n 1 (Rattus norvegicus allergen 1), the product of the rat Mup13 gene. Mice are fearful of these Mups even when they are made in bacteria, but mutant animals that are unable to detect the Mups showed no fear of rats, demonstrating their importance in initiating fearful behaviour. It is not known exactly how Mups from different species initiate disparate behaviours, but mouse Mups and predator Mups have been shown to activate unique patterns of sensory neurons in the nose of recipient mice. This implies the mouse perceives them differently, via distinct neural circuits. The pheromone receptors responsible for Mup detection are also unknown, though they are thought be members of the V2R receptor class.
between Mups and structurally similar human lipocalins has been proposed as a possible explanation. The protein product of the mouse Mup17 gene, known as Mus m 1, Ag1 or MA1, accounts for much of the allergenic properties of mouse urine. The protein is extremely stable in the environment; studies have found 95% of inner city homes, and 82% of all types of homes in the United States have detectable levels in at least one room. Similarly, Rat n 1 is a known human allergen. A US study found its presence in 33% of inner city homes, and 21% percent of occupants were sensitized to the allergen. Exposure and sensitization to rodent Mup proteins is considered a risk factor for childhood asthma
, and is a leading cause of laboratory animal allergy
(LAA)—an occupational disease of laboratory animal technicians and scientists. One study found that two-thirds of laboratory workers who had developed asthmatic reactions to animals had antibodies to Rat n 1.
Mup genes from other mammals also encode allergenic proteins, for example Fel d 4 is primarily produced in the submandibular salivary gland
and is deposited onto dander
as the cat grooms itself. A study found that 63% of cat allergic people have antibodies against the protein. Most had higher titres of antibodies against Fel d 4 than against Fel d 1
, another prominent cat allergen. Likewise, Equ c1 (Equus caballus allergen 1) is the protein product of a horse Mup gene that is found in the liver, sublingual and submaxillary salivary glands. It is responsible for about 80% of the antibody response in patients who are chronically exposed to horse allergens.
than their lean siblings. When they delivered Mup protein directly into the bloodstream of these mice, they observed an increase in energy expenditure, physical activity and body temperature and a corresponding decrease in glucose intolerance and insulin resistance
. They propose that Mups' beneficial effects on energy metabolism occurs by enhancing mitochondrial function in skeletal muscle. Another study found Mups were reduced in diet-induced obese mice. In this case, the presence of Mups in the bloodstream of mice restricted glucose production by directly inhibiting the expression of genes
in the liver.
Protein subfamily
Protein subfamily is a level of protein classification, especially protein 3D structures. It is under protein family. Protein family in SCOP means the members are all related evolutionarily and they share very similar structures with functional similarities...
of proteins found in abundance in the urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
and other secretion
Secretion
Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...
s of many animals. Mups provide a small range of identifying information about the donor animal, when detected by the vomeronasal organ
Vomeronasal organ
The vomeronasal organ , or Jacobson's organ, is an auxiliary olfactory sense organ that is found in many animals. It was discovered by Frederik Ruysch and later by Ludwig Jacobson in 1813....
of the receiving animal. They belong to a larger family
Protein family
A protein family is a group of evolutionarily-related proteins, and is often nearly synonymous with gene family. The term protein family should not be confused with family as it is used in taxonomy....
of proteins known as lipocalin
Lipocalin
The lipocalins are a family of proteins which transport small hydrophobic molecules such as steroids, bilins, retinoids, and lipids. They share limited regions of sequence homology and a common tertiary structure architecture...
s. Mups are encoded by a cluster of genes
Gene cluster
A gene cluster is a set of two or more genes that serve to encode for the same or similar products. Because populations from a common ancestor tend to possess the same varieties of gene clusters, they are useful for tracing back recent evolutionary history...
, located adjacent to each other on a single stretch of DNA, that varies greatly in number between species: from at least 21 functional genes in mice to none in humans. Mup proteins form a characteristic glove
Glove
A glove is a garment covering the hand. Gloves have separate sheaths or openings for each finger and the thumb; if there is an opening but no covering sheath for each finger they are called "fingerless gloves". Fingerless gloves with one large opening rather than individual openings for each...
shape, encompassing a ligand
Ligand (biochemistry)
In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein.The binding occurs by intermolecular forces, such as ionic bonds, hydrogen...
-binding pocket that accommodates specific small, organic chemicals.
Urinary proteins were first reported in rodents in 1932, during studies by Thomas Addis
Thomas Addis
Thomas Addis was a physician-scientist who made important contributions to the understanding of how blood clots. He was a pioneer in the field of nephrology, the branch of internal medicine that deals with diseases of the kidney...
into the cause of proteinuria
Proteinuria
Proteinuria means the presence of anexcess of serum proteins in the urine. The protein in the urine often causes the urine to become foamy, although foamy urine may also be caused by bilirubin in the urine , retrograde ejaculation, pneumaturia due to a fistula, or drugs such as pyridium.- Causes...
. They are potent human allergen
Allergen
An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....
s, and are largely responsible for a number of animal allergies
Animal allergy
In medicine, animal allergy is hypersensitivity to certain substances produced by animals, such as the proteins in animal hair and saliva. It is a common type of allergy.-Causes:...
, including to cats, horses and rodents. Their endogenous
Endogenous
Endogenous substances are those that originate from within an organism, tissue, or cell. Endogenous retroviruses are caused by ancient infections of germ cells in humans, mammals and other vertebrates...
function within an animal is unknown, but may involve regulating energy expenditure. However, as secreted proteins they play multiple roles in chemical communication between animals, functioning as pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
transporters and stabilizers in rodents and pigs. Mups can also act as protein pheromones themselves. They have been demonstrated to promote aggression
Aggression
In psychology, as well as other social and behavioral sciences, aggression refers to behavior between members of the same species that is intended to cause humiliation, pain, or harm. Ferguson and Beaver defined aggressive behavior as "Behavior which is intended to increase the social dominance of...
in male mice, and one specific Mup protein found in male mouse urine is sexually attractive to female mice. Mups can also function as signals between different species
Kairomone
A kairomone is a semiochemical, emitted by an organism, which mediates interspecific interactions in a way that benefits an individual of another species which receives it, without benefiting the emitter. This "eavesdropping" is often disadvantageous to the producer...
: mice display an instinctive fear response on the detection of Mups derived from predators such as cats and rats.
Discovery
Humans in good health excrete urine that is largely free of protein. Therefore since 1827 physicians and scientists have been interested in proteinuriaProteinuria
Proteinuria means the presence of anexcess of serum proteins in the urine. The protein in the urine often causes the urine to become foamy, although foamy urine may also be caused by bilirubin in the urine , retrograde ejaculation, pneumaturia due to a fistula, or drugs such as pyridium.- Causes...
, the excess of protein in human urine, as an indicator of kidney disease. To better understand the etiology
Etiology
Etiology is the study of causation, or origination. The word is derived from the Greek , aitiologia, "giving a reason for" ....
of proteinuria, some scientists attempted to study the phenomenon in laboratory animals
Animal testing
Animal testing, also known as animal experimentation, animal research, and in vivo testing, is the use of non-human animals in experiments. Worldwide it is estimated that the number of vertebrate animals—from zebrafish to non-human primates—ranges from the tens of millions to more than 100 million...
. Between 1932 and 1933 a number of scientists, including Thomas Addis
Thomas Addis
Thomas Addis was a physician-scientist who made important contributions to the understanding of how blood clots. He was a pioneer in the field of nephrology, the branch of internal medicine that deals with diseases of the kidney...
, independently reported the surprising finding that some healthy rodents have protein in their urine. However, it was not until the 1960s that the major urinary proteins of mice and rats were first described in detail. It was found that the proteins are primarily made in the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
of males and secreted through the kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
s into the urine in large quantities (milligrams per day).
Since they were named, the proteins have been found to be differentially expressed in other glands
Exocrine gland
Exocrine glands are a type of ductal glands that secrete their products into ducts that lead directly into the external environment...
that secrete products directly into the external environment. These include lacrimal
Lacrimal gland
The lacrimal glands are paired almond-shaped glands, one for each eye, that secrete the aqueous layer of the tear film. They are situated in the upper, outer portion of each orbit, in the lacrimal fossa of the orbit formed by the frontal bone. Inflammation of the lacrimal glands is called...
, parotid, submaxillary, sublingual
Sublingual gland
The sublingual glands are salivary glands in the mouth.They lie anterior to the submandibular gland under the tongue, beneath the mucous membrane of the floor of the mouth.They are drained by 8-20 excretory ducts called the ducts of Rivinus....
, preputial
Preputial gland
Preputial glands are exocrine glands that are located in front of the genitals of some mammals and produce pheromones. The preputial glands of female animals are sometimes called clitoral glands....
and mammary glands. In some species, such as cats and pigs, Mups appear not to be expressed in urine at all and are mainly found in saliva. Sometimes the term urinary Mups (uMups) is used to distinguish those Mups expressed in urine from those in other tissues.
Mup genes
Between 1979 and 1981, it was estimated that Mups are encoded by a gene familyGene family
A gene family is a set of several similar genes, formed by duplication of a single original gene, and generally with similar biochemical functions...
of between 15 and 35 genes and pseudogene
Pseudogene
Pseudogenes are dysfunctional relatives of known genes that have lost their protein-coding ability or are otherwise no longer expressed in the cell...
s in the mouse and by an estimated 20 genes in the rat. In 2008 a more precise number of Mup genes in a range of species was determined by analyzing the DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
of whole genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
s.
Rodents
The mouse reference genomeReference genome
A reference genome is a digital nucleic acid sequence database, assembled by scientists as a representative example of a species' genetic code. As they are often assembled from the sequencing of DNA from a number of donors, reference genomes do not accurately represent the genetic code of any...
has at least 21 distinct Mup genes (with open reading frame
Open reading frame
In molecular genetics, an open reading frame is a DNA sequence that does not contain a stop codon in a given reading frame.Normally, inserts which interrupt the reading frame of a subsequent region after the start codon cause frameshift mutation of the sequence and dislocate the sequences for stop...
s), and a further 21 Mup pseudogenes (with reading frame
Reading frame
In biology, a reading frame is a way of breaking a sequence of nucleotides in DNA or RNA into three letter codons which can be translated in amino acids. There are 3 possible reading frames in an mRNA strand: each reading frame corresponding to starting at a different alignment...
s disrupted by a nonsense mutation
Nonsense mutation
In genetics, a nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon, or a nonsense codon in the transcribed mRNA, and in a truncated, incomplete, and usually nonfunctional protein product. It differs from a missense mutation, which is a point mutation...
or an incomplete gene duplication
Gene duplication
Gene duplication is any duplication of a region of DNA that contains a gene; it may occur as an error in homologous recombination, a retrotransposition event, or duplication of an entire chromosome.The second copy of the gene is often free from selective pressure — that is, mutations of it have no...
). They are all clustered together, arrayed side by side across 1.92 megabases of DNA on chromosome 4. The 21 functional genes have been divided into two sub-classes based on position and sequence similarity: 6 peripheral Class A Mups, and 15 central Class B Mups. The central Class B Mup gene cluster formed through a number of sequential duplications from one of the Class A Mups. As all the Class B genes are almost identical to each other, researchers have concluded that these duplications occurred very recently in mouse evolution. Indeed, the repetitive structure of these central Mup genes means they are likely to be unstable and may vary in number among wild mice. The Class A Mups are more different from each other and are therefore likely to be more stable, older genes but what, if any, functional differences the classes have are unknown. The similarity between the genes makes the region difficult to study using current DNA sequencing technology
Shotgun sequencing
In genetics, shotgun sequencing, also known as shotgun cloning, is a method used for sequencing long DNA strands. It is named by analogy with the rapidly-expanding, quasi-random firing pattern of a shotgun....
. Consequently the Mup gene cluster is one of the few parts of the mouse whole genome sequence with gaps remaining, and further genes may remain undiscovered.
Rat urine also contains homologous urinary proteins; although they were originally given a different name, α2u-globulins
Alpha globulin
Alpha Globulins are a group of globular proteins in plasma, which are highly mobile in alkaline or electrically charged solutions. They inhibit certain blood protease and inhibitor activity.-Alpha 1 globulins:*α1-antitrypsin*Alpha 1-antichymotrypsin...
, they have since become known as rat Mups. Rats have 9 distinct Mup genes and a further 13 pseudogenes clustered together across 1.1 megabases of DNA on chromosome 5. Like in mice, the cluster formed by multiple duplications. However, this occurred independently of the duplications in mice, meaning that both rodent species expanded their Mup gene families separately, but in parallel
Parallel evolution
Parallel evolution is the development of a similar trait in related, but distinct, species descending from the same ancestor, but from different clades.-Parallel vs...
.
Nonrodents
Most other mammals studied, including the pig, cow, cat, dog, bushbaby, macaque, chimpanzee and orangutan, have a single Mup gene. Some, however, have an expanded number: horses have three Mup genes and gray mouse lemurGray Mouse Lemur
The gray mouse lemur , or lesser mouse lemur, is a small lemur, a type of strepsirrhine primate, found only on the island of Madagascar. Weighing , it is the largest of the mouse lemurs , a group which include the smallest primates in the world...
s have at least two. Insects, fish, amphibia, birds and marsupial
Marsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
s appear to have disrupted synteny
Synteny
In classical genetics, synteny describes the physical co-localization of genetic loci on the same chromosome within an individual or species. The concept is related to genetic linkage: Linkage between two loci is established by the observation of lower-than-expected recombination frequencies...
at the chromosomal position of the Mup gene cluster, suggesting the gene family may be specific to placental mammals. Humans are the only placental mammals found not to have any active Mup genes; instead they have a single Mup pseudogene containing a mutation that causes missplicing
RNA splicing
In molecular biology and genetics, splicing is a modification of an RNA after transcription, in which introns are removed and exons are joined. This is needed for the typical eukaryotic messenger RNA before it can be used to produce a correct protein through translation...
, rendering it dysfunctional.
Transport proteins
Mups are members of a large family of low-molecular weight (~19 kDaKDA
KDA may refer to:* Karachi Development Authority* Kongsberg Defence & Aerospace* Kotelawala Defence Academy* Kramer Design Associates* Lithium diisopropylamide, KDA is the potassium analogue of lithium diisopropylamideOr kDa may refer to:...
) proteins known as lipocalin
Lipocalin
The lipocalins are a family of proteins which transport small hydrophobic molecules such as steroids, bilins, retinoids, and lipids. They share limited regions of sequence homology and a common tertiary structure architecture...
s. They have a characteristic structure
Tertiary structure
In biochemistry and molecular biology, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates.-Relationship to primary structure:...
of eight beta sheet
Beta sheet
The β sheet is the second form of regular secondary structure in proteins, only somewhat less common than the alpha helix. Beta sheets consist of beta strands connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet...
s arranged in an anti-parallel
Antiparallel (biochemistry)
In biochemistry, two molecules are antiparallel if they run side-by-side in opposite directions or when both strands are complimentary to each other....
beta barrel open on one face, with alpha helices
Alpha helix
A common motif in the secondary structure of proteins, the alpha helix is a right-handed coiled or spiral conformation, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...
at both ends. Consequently, they form a characteristic glove shape, encompassing a cup-like pocket
Calyx (zoology)
-Cnidarians:The spicules containing the basal portion of the upper tentacular part of the polyp of some soft corals .-Entoprocta:A body part of the Entoprocta from which tentacles arise and the mouth and anus are located.-Echinoderms:...
that binds small organic chemicals with high affinity. A number of these ligands bind to mouse Mups, including 2-sec-butyl-4,5-dihydrothiazole
Thiazole
Thiazole, or 1,3-thiazole, is a heterocyclic compound that contains both sulfur and nitrogen; the term 'thiazole' also refers to a large family of derivatives. Thiazole itself is a pale yellow liquid with a pyridine-like odor and the molecular formula C3H3NS...
(abbreviated as SBT or DHT), 6-hydroxy-6-methyl-3-heptanone
Heptanone
Heptanone may refer to these isomeric chemical compounds:* 2-Heptanone* 4-Heptanone...
(HMH) and 2,3 dihydro-exo-brevicomin (DHB). These are all urine-specific chemicals that have been shown to act as pheromones—molecular signals excreted by one individual that trigger an innate behavioural response in another member of the same species. Mouse Mups have also been shown to function as pheromone stabilizers, providing a slow release mechanism that extends the potency of volatile pheromones in male urine scent marks. Given the diversity of Mups in rodents, it was originally thought that different Mups may have differently shaped binding pockets and therefore bind different pheromones. However, detailed studies found that most variable sites
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
are located on the surface of the proteins, and appear to have little effect on ligand binding.
Rat Mups bind different small chemicals. 1-Chlorodecane
Decane
Decane is an alkane hydrocarbon with the chemical formula CH38CH3.75 structural isomers of decane exist, all of which are flammable liquids. Decane is one of the components of gasoline . Like other alkanes, it is nonpolar and therefore will not dissolve in polar liquids such as water...
is the most common ligand, with 2-methyl-N-phenyl-2-propenamide
Acrylamide
Acrylamide is a chemical compound with the chemical formula C3H5NO. Its IUPAC name is prop-2-enamide. It is a white odourless crystalline solid, soluble in water, ethanol, ether, and chloroform. Acrylamide is incompatible with acids, bases, oxidizing agents, iron, and iron salts...
, hexadecane
Hexadecane
Hexadecane is an alkane hydrocarbon with the chemical formula C16H34. Hexadecane consists of a chain of 16 carbon atoms, with three hydrogen atoms bonded to the two end carbon atoms, and two hydrogens bonded to each of the 14 other carbon atoms.Cetane is often used as a short-hand for cetane...
and 2,6,11-trimethyl decane found to be less prominent. Rat Mups also bind limonene
Limonene
Limonene is a colourless liquid hydrocarbon classified as a cyclic terpene. The more common D isomer possesses a strong smell of oranges. It is used in chemical synthesis as a precursor to carvone and as a renewably-based solvent in cleaning products....
-1,2-epoxide, resulting in a disease of the host's kidney, hyaline
Hyaline
The term hyaline denotes a substance with a glass-like appearance.-Histopathology:In histopathological medical usage, a hyaline substance appears glassy and pink after being stained with haematoxylin and eosin — usually it is an acellular, proteinaceous material...
-droplet nephropathy
Nephropathy
Nephropathy refers to damage to or disease of the kidney. An older term for this is nephrosis.-Causes:Causes of nephropathy include administration of analgesics, xanthine oxidase deficiency, and long-term exposure to lead or its salts...
, that progresses to cancer. Other species do not develop this disorder because their Mups do not bind that particular chemical. Accordingly, when transgenic mice
Knockout mouse
A knockout mouse is a genetically engineered mouse in which researchers have inactivated, or "knocked out," an existing gene by replacing it or disrupting it with an artificial piece of DNA...
were engineered to express the rat Mup their kidneys developed the disease.
The Mup found in pigs, named salivary lipocalin (SAL), is expressed in the salivary gland of males where it tightly binds androstenone
Androstenone
Androstenone is a steroid found in both male and female sweat and urine. It is also found in boar's saliva, and in celery cytoplasm. Androstenone was the first mammalian pheromone to be identified. It is found in high concentrations in the saliva of male pigs, and, when sniffed by a female pig...
and androstenol
Androstenol
Androstenol is a sex pheromone in pigs, possessing a musk-like odor.It is found in large quantities in boar saliva, but also in smaller quantities in human sweat glands. It is analogous to sex hormones yet has minimal or no androgenic activity...
, both pheromones that cause female pigs to assume a mating stance
Lordosis behavior
Lordosis behavior, or mammalian lordosis, is a sexual response in mammals, such as mice and cats, that consists of a ventral arching of the spine. During lordosis, the spine curves so that the apex points in the ventral direction. That is, the spine arches inward toward the abdomen.Lordosis aids in...
.
Isothermal titration calorimetry
Isothermal Titration Calorimetry
Isothermal titration calorimetry is a physical technique used to determine the thermodynamic parameters of interactions in solution. It is most often used to study the binding of small molecules to larger macromolecules .-Thermodynamic measurements:ITC is a quantitative technique that can...
studies performed with Mups and associated ligands (pyrazines, alcohols, thiazolines, 6-hydroxy-6-methyl-3-heptanone, and N-phenylnapthylamine,) revealed an unusual binding phenomena. The active site
Active site
In biology the active site is part of an enzyme where substrates bind and undergo a chemical reaction. The majority of enzymes are proteins but RNA enzymes called ribozymes also exist. The active site of an enzyme is usually found in a cleft or pocket that is lined by amino acid residues that...
has been found to be suboptimally hydrated, resulting in ligand binding being driven by enthalpic
Enthalpy
Enthalpy is a measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.Enthalpy is a...
dispersion forces. This is contrary to most other proteins, which exhibit entropy
Entropy
Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...
-driven binding forces from the reorganisation of water molecules. This unusual process has been termed the "nonclassical hydrophobic effect."
Pheromones
Studies have sought to find the precise function of Mups in pheromone communication. Mup proteins have been shown to promote pubertyPuberty
Puberty is the process of physical changes by which a child's body matures into an adult body capable of reproduction, as initiated by hormonal signals from the brain to the gonads; the ovaries in a girl, the testes in a boy...
and accelerate the estrus cycle in female mice, inducing the Vandenbergh
Vandenbergh effect
The Vandenbergh effect is a phenomenon reported by J.G. Vandenbergh et al. in 1975, in which an early induction of the first estrous cycle in prepubertal female mice occurs as a result of exposure to the pheromone-laden urine of a sexually mature male mouse.Physiologically, the exposure to male...
and Whitten effect
Whitten effect
The Whitten effect is a phenomenon observed by Wesley K. Whitten , whereby male mouse pheromone-laden urine synchronizes the estrus cycle "among unisexually grouped females."...
s. However, in both cases the Mups had to be presented to the female dissolved in male urine, indicating that the protein requires some urinary context to function. In 2007 Mups normally found in male mouse urine were made in transgenic bacteria, and therefore created devoid of the chemicals they normally bind. These Mups were shown to be sufficient to promote aggressive
Aggressive
“Aggressive” is a New York-based Grammy award-winning music video and commercial directing team of Alex Topaller and Daniel Shapiro.Aggressive has been described by Movie Creation Mag as “having a fascination with the wonderful, in the likes of the surrealist Rafal Olbinski” and “tenacious about...
behaviour in males, even in the absence of urine. In addition, Mups made in bacteria were found to activate olfactory sensory neurons in the vomeronasal organ (VNO), a subsystem of the nose known to detect pheromones via specific sensory receptor
Sensory receptor
In a sensory system, a sensory receptor is a sensory nerve ending that responds to a stimulus in the internal or external environment of an organism...
s, of mice and rats. Together, this demonstrated that Mup proteins can act as pheromones themselves, independent of their ligands.
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
is complex, but at least three hormones—testosterone
Testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
, growth hormone
Growth hormone
Growth hormone is a peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals. Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior...
and thyroxine
Thyroxine
Thyroxine, or 3,5,3',5'-tetraiodothyronine , a form of thyroid hormones, is the major hormone secreted by the follicular cells of the thyroid gland.-Synthesis and regulation:...
—are known to positively influence the production of Mups in mice. Wild house mouse
House mouse
The house mouse is a small rodent, a mouse, one of the most numerous species of the genus Mus.As a wild animal the house mouse mainly lives associated with humans, causing damage to crops and stored food....
urine contains variable combinations of four to seven distinct Mup proteins per mouse. Some inbred laboratory mouse strains
Inbred strain
Inbred strains are individuals of a particular species which are nearly identical to each other in genotype due to long inbreeding. Inbred strains of animals are frequently used in laboratories for experiments where for reproducibility of conclusions all the test animals should be as similar as...
, such as BALB/c
BALB/c
BALB/c is an albino, laboratory-bred strain of the House Mouse from which a number of common substrains are derived. Now over 200 generations from their origin in New York in 1920, BALB/c mice are distributed globally, and are among the most widely used inbred strains used in animal...
and C57BL/6, also have different proteins expressed in their urine. However, unlike wild mice, different individuals from the same strain express the same protein pattern, an artifact of many generations of inbreeding
Inbreeding
Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...
. One unusual Mup is less variable than the others: it is consistently produced by a high proportion of wild male mice and is almost never found in female urine. When this Mup was made in bacteria and used in behavioural testing, it was found to attract female mice. Other Mups were tested but they did not have the same attractive qualities, suggesting the male-specific Mup acts as a sex pheromone. Scientists named this Mup darcin as a humorous reference to Fitzwilliam Darcy
Fitzwilliam Darcy
Fitzwilliam Darcy, generally referred to as Mr Darcy, is one of the two central characters in Jane Austen's novel Pride and Prejudice. He is an archetype of the aloof romantic hero, and a romantic interest of Elizabeth Bennet, the novel's protagonist...
, the romantic hero from Pride and Prejudice
Pride and Prejudice
Pride and Prejudice is a novel by Jane Austen, first published in 1813. The story follows the main character Elizabeth Bennet as she deals with issues of manners, upbringing, morality, education and marriage in the society of the landed gentry of early 19th-century England...
. Taken together, the complex patterns of Mups produced has the potential to provide a range information about the donor animal, such as gender
Gender
Gender is a range of characteristics used to distinguish between males and females, particularly in the cases of men and women and the masculine and feminine attributes assigned to them. Depending on the context, the discriminating characteristics vary from sex to social role to gender identity...
, fertility, social dominance
Dominance hierarchy
A dominance hierarchy is the organization of individuals in a group that occurs when competition for resources leads to aggression...
, age, genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
or kinship
Kinship
Kinship is a relationship between any entities that share a genealogical origin, through either biological, cultural, or historical descent. And descent groups, lineages, etc. are treated in their own subsections....
. Wild mice (unlike laboratory mice that are genetically identical and which therefore also have identical patterns of Mups in the urine) have individual patterns of Mup expression in their urine that act as a "barcode
Barcode
A barcode is an optical machine-readable representation of data, which shows data about the object to which it attaches. Originally barcodes represented data by varying the widths and spacings of parallel lines, and may be referred to as linear or 1 dimensional . Later they evolved into rectangles,...
" to uniquely identify the owner of a scent mark.
Kairomones
In addition to serving as social cues between members of the same species, Mups can act as kairomoneKairomone
A kairomone is a semiochemical, emitted by an organism, which mediates interspecific interactions in a way that benefits an individual of another species which receives it, without benefiting the emitter. This "eavesdropping" is often disadvantageous to the producer...
s—chemical signals that transmit information between species. Mice are instinctively afraid of the smell of their natural predators, including cats and rats. This occurs even in laboratory mice that have been isolated from predators for hundreds of generations. When the chemical cues responsible for the fear
Fear
Fear is a distressing negative sensation induced by a perceived threat. It is a basic survival mechanism occurring in response to a specific stimulus, such as pain or the threat of danger...
response were purified from cat saliva and rat urine, two homologous protein signals were identified: Fel d 4 (Felis domesticus allergen 4), the product of the cat Mup gene, and Rat n 1 (Rattus norvegicus allergen 1), the product of the rat Mup13 gene. Mice are fearful of these Mups even when they are made in bacteria, but mutant animals that are unable to detect the Mups showed no fear of rats, demonstrating their importance in initiating fearful behaviour. It is not known exactly how Mups from different species initiate disparate behaviours, but mouse Mups and predator Mups have been shown to activate unique patterns of sensory neurons in the nose of recipient mice. This implies the mouse perceives them differently, via distinct neural circuits. The pheromone receptors responsible for Mup detection are also unknown, though they are thought be members of the V2R receptor class.
Allergens
Along with other members of the lipocalin protein family, major urinary proteins can be potent allergens to humans. The reason for this is not known, however molecular mimicryMolecular mimicry
Molecular mimicry is defined as the theoretical possibility that sequence similarities between foreign and self-peptides are sufficient to result in the cross-activation of autoreactive T or B cells by pathogen-derived peptides...
between Mups and structurally similar human lipocalins has been proposed as a possible explanation. The protein product of the mouse Mup17 gene, known as Mus m 1, Ag1 or MA1, accounts for much of the allergenic properties of mouse urine. The protein is extremely stable in the environment; studies have found 95% of inner city homes, and 82% of all types of homes in the United States have detectable levels in at least one room. Similarly, Rat n 1 is a known human allergen. A US study found its presence in 33% of inner city homes, and 21% percent of occupants were sensitized to the allergen. Exposure and sensitization to rodent Mup proteins is considered a risk factor for childhood asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
, and is a leading cause of laboratory animal allergy
Laboratory animal allergy
Laboratory animal allergy is an occupational disease of laboratory animal technicians and scientists. It manifests as an allergic response to animal urine, specifically the major urinary proteins of rodents, and can lead to the development of asthma...
(LAA)—an occupational disease of laboratory animal technicians and scientists. One study found that two-thirds of laboratory workers who had developed asthmatic reactions to animals had antibodies to Rat n 1.
Mup genes from other mammals also encode allergenic proteins, for example Fel d 4 is primarily produced in the submandibular salivary gland
Submandibular gland
The paired submandibular glands are salivary glands located beneath the floor of the mouth. In humans, they account for 70% of the salivary volume and weigh about 15 grams. Unstimulated in humans, the percentage contribution to whole saliva; ~25% Parotid, Submandibular and Sublingual ~ 67% and...
and is deposited onto dander
Dander
Dander is an informal term for a material shed from the body of various animals, similar to dandruff. It may contain scales of dried skin and hair, or feathers. It is a cause of allergies in humans....
as the cat grooms itself. A study found that 63% of cat allergic people have antibodies against the protein. Most had higher titres of antibodies against Fel d 4 than against Fel d 1
Fel d 1
Fel d 1 is a protein that in cats is encoded by the CH1 and CH2 genes.Fel d 1, produced largely by cat saliva and sebaceous glands, is the primary allergen present on cats. The protein is of an unknown function to the animal but causes an IgG or IgE reaction in sensitive humans...
, another prominent cat allergen. Likewise, Equ c1 (Equus caballus allergen 1) is the protein product of a horse Mup gene that is found in the liver, sublingual and submaxillary salivary glands. It is responsible for about 80% of the antibody response in patients who are chronically exposed to horse allergens.
Metabolism
While the detection of Mups excreted by other animals has been well studied, the functional role in the producing animal is less clear. However, in 2009, Mups were shown to be associated with the regulation of energy expenditure in mice. Scientists found that genetically induced obese, diabetic mice produce thirty times less Mup RNARNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
than their lean siblings. When they delivered Mup protein directly into the bloodstream of these mice, they observed an increase in energy expenditure, physical activity and body temperature and a corresponding decrease in glucose intolerance and insulin resistance
Insulin resistance
Insulin resistance is a physiological condition where the natural hormone insulin becomes less effective at lowering blood sugars. The resulting increase in blood glucose may raise levels outside the normal range and cause adverse health effects, depending on dietary conditions. Certain cell types...
. They propose that Mups' beneficial effects on energy metabolism occurs by enhancing mitochondrial function in skeletal muscle. Another study found Mups were reduced in diet-induced obese mice. In this case, the presence of Mups in the bloodstream of mice restricted glucose production by directly inhibiting the expression of genes
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...
in the liver.
See also
- Cis-vaccenyl acetate, an insect aggression pheromone.
- Major histocompatibility complexMajor histocompatibility complexMajor histocompatibility complex is a cell surface molecule encoded by a large gene family in all vertebrates. MHC molecules mediate interactions of leukocytes, also called white blood cells , which are immune cells, with other leukocytes or body cells...
, peptides also implicated in individual recognition in mice. - Proteins produced and secreted by the liverProteins produced and secreted by the liverThe liver plays the major role in producing proteins that are secreted into the blood, including major plasma proteins, factors in hemostasis and fibrinolysis, carrier proteins, hormones, prohormones and apolipoproteins:-Major plasma proteins:...
.
External links
- Scent of a Rodent, The Why Files – The Science Behind The News, a video describing the research that determined Mups were kairomones