Globin
Encyclopedia
Globins are a related family of proteins
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....

, which are thought to share a common ancestor. These proteins all incorporate the globin fold, a series of eight alpha helical segments
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...

. Two prominent members of this family include myoglobin
Myoglobin
Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the...

 and hemoglobin
Hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

, which both bind the heme
Heme
A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...

 (also haem) prosthetic group. Both these proteins are reversible oxygen binders.

Globins are haem-containing protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s involved in binding
Binding (molecular)
Molecular binding is an attractive interaction between two molecules which results in a stable association in which the molecules are in close proximity to each other...

 and/or transporting oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

. They belong to a very large and well studied family that is widely distributed in many organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

s.

Types

Globins have evolved
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

 from a common ancestor and can be divided into three groups: single-domain globins, and two types of chimeric
Fusion protein
Fusion proteins or chimeric proteins are proteins created through the joining of two or more genes which originally coded for separate proteins. Translation of this fusion gene results in a single polypeptide with functional properties derived from each of the original proteins...

 globins, flavohaemoglobins and globin-coupled sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...

s. Bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 have all three types of globins, while archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...

 lack flavohaemoglobins, and eukaryotes lack globin-coupled sensors. Several functionally different haemoglobins can coexist in the same species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

.

Subfamilies

  • Leghaemoglobin 
  • Myoglobin
    Myoglobin
    Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the...

     
  • Erythrocruorin
    Erythrocruorin
    Erythrocruorin is a large oxygen-carrying protein, whose molecular mass is greater than 3.5 million Daltons. It is related to the similar chlorocruorin. It is found in many annelids.- References :*, PNAS June 20, 2000. Accessed July 17, 2007....

     
  • Haemoglobin, beta
    HBB
    Beta globin Beta globin Beta globin (HBB, β-globinprotin that, along with alpha globin (HBA), makes up the most common form of hemoglobin in adult humans. The normal adult hemoglobin tetramer consists of two alpha chains and two beta chains.-Gene locus:...

     
  • Haemoglobin, alpha
    HBA1
    Hemoglobin, alpha 1, also known as HBA1, is a human gene encoding the hemoglobin protein.-Interactions:Hemoglobin, alpha 1 has been shown to interact with HBB. Interactions between the N-terminal amino groups of the alpha-subunits and the C-terminal histidine of the β-subunits participate in ion...

     
  • Myoglobin, trematode type 
  • Globin, nematode 
  • Globin, lamprey/hagfish type 
  • Globin, annelid-type 
  • Haemoglobin, extracellular 

Examples

Human genes encoding globin proteins include:
  • CYGB
    Cytoglobin
    Cytoglobin is the protein product of CYGB, a human and mammalian gene.Cytoglobin is a globin molecule located in the brain and most notably utilized in marine mammals. It is thought to be a method of protection under conditions of hypoxia. The predicted function of cytoglobin is the transfer of...

  • HBA1, HBA2
    HBA2
    Hemoglobin, alpha 2 also known as HBA2 is a gene that in humans codes for the alpha globin chain of hemoglobin.- Function :The human alpha globin gene cluster located on chromosome 16 spans about 30 kb and includes seven alpha like globin genes and pseudogenes: 5'- HBZ - HBZP1 - HBM - HBAP1 - HBA2...

    , HBB
    HBB
    Beta globin Beta globin Beta globin (HBB, β-globinprotin that, along with alpha globin (HBA), makes up the most common form of hemoglobin in adult humans. The normal adult hemoglobin tetramer consists of two alpha chains and two beta chains.-Gene locus:...

    , HBD
    HBD
    Hemoglobin subunit delta is a protein that in humans is encoded by the HBD gene.-Further reading:...

    , HBE1
    HBE1
    Hemoglobin subunit epsilon is a protein that in humans is encoded by the HBE1 gene.-Further reading:...

    , HBG1
    HBG1
    Hemoglobin subunit gamma-1 is a protein that in humans is encoded by the HBG1 gene.-Further reading:...

    , HBG2
    HBG2
    Hemoglobin subunit gamma-2 is a protein that in humans is encoded by the HBG2 gene.-Further reading:...

    , HBM
    Mu hemoglobin
    Mu hemoglobin is a protein which in humans is encoded by the HBM gene....

    , HBQ1
    HBQ1
    Hemoglobin subunit theta-1 is a protein that in humans is encoded by the HBQ1 gene.-Further reading:...

    , HBZ
    HBZ
    Hemoglobin subunit zeta is a protein that in humans is encoded by the HBZ gene.-Further reading:...

    , MB
    Myoglobin
    Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the...



The globins include:
  • Haemoglobin (Hb)

  • Myoglobin
    Myoglobin
    Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the...

     (Mb)

  • Neuroglobin: a myoglobin-like haemprotein expressed
    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 vertebrate brain
    Brain
    The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

     and retina, where it is involved in neuroprotection from damage due to hypoxia
    Hypoxia (medical)
    Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

     or ischemia
    Ischemia
    In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...

    . Neuroglobin belongs to a branch of the globin family that diverged early in evolution
    Evolution
    Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

    .

  • Cytoglobin
    Cytoglobin
    Cytoglobin is the protein product of CYGB, a human and mammalian gene.Cytoglobin is a globin molecule located in the brain and most notably utilized in marine mammals. It is thought to be a method of protection under conditions of hypoxia. The predicted function of cytoglobin is the transfer of...

    : an oxygen sensor expressed
    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 multiple tissues
    Biological tissue
    Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...

    . Related to neuroglobin.

  • Erythrocruorin
    Erythrocruorin
    Erythrocruorin is a large oxygen-carrying protein, whose molecular mass is greater than 3.5 million Daltons. It is related to the similar chlorocruorin. It is found in many annelids.- References :*, PNAS June 20, 2000. Accessed July 17, 2007....

    : highly cooperative extracellular
    Extracellular
    In cell biology, molecular biology and related fields, the word extracellular means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid...

     respiratory proteins found in annelid
    Annelid
    The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...

    s and arthropod
    Arthropod
    An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

    s that are assembled from as many as 180 subunit into hexagonal bilayers.

  • Leghaemoglobin (legHb or symbiotic
    Symbiosis
    Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...

     Hb): occurs in the root
    Root
    In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

     nodules of leguminous plants, where it facilitates the diffusion
    Diffusion
    Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

     of oxygen to symbiotic bacteriods in order
    Order (biology)
    In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

     to promote nitrogen
    Nitrogen
    Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

     fixation .

  • Non-symbiotic haemoglobin (NsHb): occurs in non-leguminous plants, and can be over-expressed in stressed plants .

  • Flavohaemoglobins (FHb): chimeric, with an N-terminal globin domain and a C-terminal ferredoxin
    Ferredoxin
    Ferredoxins are iron-sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co...

     reductase-like NAD/FAD-binding domain. FHb provides protection against nitric oxide
    Nitric oxide
    Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...

     via its C-terminal domain, which transfers electron
    Electron
    The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

    s to haem in the globin.

  • Globin E: a globin responsible for storing and delivering oxygen to the retina in birds

  • Globin-coupled sensors: chimeric, with an N-terminal myoglobin-like domain and a C-terminal domain that resembles the cytoplasm
    Cytoplasm
    The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

    ic signalling domain of bacteria
    Bacteria
    Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

    l chemoreceptors. They bind oxygen, and act to initiate an aerotactic response or regulate
    Transcriptional regulation
    Transcriptional regulation is the change in gene expression levels by altering transcription rates. -Regulation of transcription:Regulation of transcription controls when transcription occurs and how much RNA is created...

     gene expression
    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...

    .

  • Protoglobin: a single domain globin found in archaea
    Archaea
    The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...

     that is related to the N-terminal domain of globin-coupled sensors.

  • Truncated 2/2 globin: lack the first helix, giving them a 2-over-2 instead of the canonical 3-over-3 alpha-helical
    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...

     sandwich fold
    Protein folding
    Protein folding is the process by which a protein structure assumes its functional shape or conformation. It is the physical process by which a polypeptide folds into its characteristic and functional three-dimensional structure from random coil....

    . Can be divided into three main groups (I, II and II) based on structural
    Secondary structure
    In biochemistry and structural biology, secondary structure is the general three-dimensional form of local segments of biopolymers such as proteins and nucleic acids...

     features.

  • HbN (or GlbN): a truncated haemoglobin-like protein that binds oxygen cooperatively with a very high affinity and a slow dissociation
    Dissociation (chemistry)
    Dissociation in chemistry and biochemistry is a general process in which ionic compounds separate or split into smaller particles, ions, or radicals, usually in a reversible manner...

     rate, which may exclude it from oxygen transport. It appears to be involved in bacterial nitric oxide detoxification and in nitrosative stress
    Stress (medicine)
    Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...

    .

  • Cyanoglobin (or GlbN): a truncated haemoprotein found in cyanobacteria that has high oxygen affinity, and which appears to serve as part of a terminal oxidase, rather than as a respiratory pigment.

  • HbO (or GlbO): a truncated haemoglobin-like protein with a lower oxygen affinity than HbN. HbO associates with the bacterial cell
    Cell (biology)
    The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

     membrane, where it significantly
    Statistical significance
    In statistics, a result is called statistically significant if it is unlikely to have occurred by chance. The phrase test of significance was coined by Ronald Fisher....

     increases oxygen uptake over membrane
    Cell membrane
    The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

    s lacking this protein. HbO appears to interact
    Protein-protein interaction
    Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...

     with a terminal oxidase, and could participate in an oxygen/electron-transfer process that facilitates oxygen transfer during aerobic metabolism.

  • Glb3: a nuclear-encoded truncated haemoglobin from plant
    Plant
    Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

    s that appears more closely related to HbO than HbN. Glb3 from Arabidopsis
    Arabidopsis thaliana
    Arabidopsis thaliana is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, arabidopsis is popular as a model organism in plant biology and genetics...

     thaliana
    (Mouse-ear cress) exhibits an unusual concentration-independent binding of oxygen and carbon dioxide
    Carbon dioxide
    Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

    .
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