Glycobiology
Encyclopedia
Defined in the broadest sense, glycobiology is the study of the structure, biosynthesis, and biology of saccharides (sugar
chains or glycans
) that are widely distributed in nature. Sugars or saccharides are essential components of all living things and aspects of the various roles they play in biology are researched in various medical, biochemical and biotechnological fields.
to recognize the coming together of the traditional disciplines of carbohydrate
chemistry and biochemistry
. This coming together was as a result of a much greater understanding of the cellular and molecular biology
of glycans. However as early as the late nineteenth century pioneering efforts were being made by Emil Fisher to establish the structure of some basic sugar molecules.
s, proteoglycan
s and glycolipid
s are the most abundant glycoconjugates found in mammalian cells. They are found predominantly on the outer cell wall and in secreted fluids. Glycoconjugates have been shown to be important in cell-cell interactions due to the presence on the cell surface of various glycan binding receptors in addition to the glycoconjugates themselves.
, analogous to genomics
and proteomics
, is the systematic study of all glycan structures of a given cell type or organism" and is a subset of glycobiology.
units may be coupled to each other in many different ways, as opposed to the amino acid
s of protein
s or the nucleotide
s in DNA
, which are always coupled together in a standard fashion. The study of glycan structures is also complicated by the lack of a direct template for their biosynthesis, contrary to the case with proteins where their amino acid sequence is determined by their corresponding gene
.
Glycans are secondary gene products and therefore are generated by the coordinated action of many enzymes in the subcellular compartments of a cell. Since the structure of a glycan may depend on the expression
, activity and accessibility of the different biosynthetic enzymes, it is not possible to use recombinant DNA
technology in order to produce large quantities of glycans for structural and functional studies as it is for proteins.
which uses three principal units: the ionizer, analyzer and detector. Fast Atom Bombardment (FAB) mass spectrometers are powerful tools for characterizing complex carbohydrates. This technique can be coupled with sensitive array detector technology.
Sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
chains or glycans
Glycans
The term glycan refers to a polysaccharide or oligosaccharide. Glycans usually consist solely of O-glycosidic linkages of monosaccharides. For example, cellulose is a glycan composed of beta-1,4-linked D-glucose, and chitin is a glycan composed of beta-1,4-linked N-acetyl-D-glucosamine...
) that are widely distributed in nature. Sugars or saccharides are essential components of all living things and aspects of the various roles they play in biology are researched in various medical, biochemical and biotechnological fields.
History
The specific term glycobiology was coined on 1 August 1988 in the Oxford English Dictionary by Prof. Raymond DwekRaymond Dwek
Professor Raymond Allen Dwek BSc DPhil DSc FRS is a scientist at the University of Oxford and founded its spin-off biotechnology company, Oxford GlycoSciences Ltd. ....
to recognize the coming together of the traditional disciplines of carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
chemistry and biochemistry
Biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
. This coming together was as a result of a much greater understanding of the cellular and molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
of glycans. However as early as the late nineteenth century pioneering efforts were being made by Emil Fisher to establish the structure of some basic sugar molecules.
Glycoconjugates
Sugars may be linked to other types of biological molecule to form glycoconjugates. The enzymatic process of glycosylation creates sugars/saccharides linked to themselves and to other molecules by the glycosidic bond, thereby producing glycans. GlycoproteinGlycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...
s, proteoglycan
Proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan chain. The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge...
s and glycolipid
Glycolipid
Glycolipids are lipids with a carbohydrate attached. Their role is to provide energy and also serve as markers for cellular recognition.-Metabolism:...
s are the most abundant glycoconjugates found in mammalian cells. They are found predominantly on the outer cell wall and in secreted fluids. Glycoconjugates have been shown to be important in cell-cell interactions due to the presence on the cell surface of various glycan binding receptors in addition to the glycoconjugates themselves.
Glycomics
"GlycomicsGlycomics
Glycomics is the comprehensive study of glycomes , including genetic, physiologic, pathologic, and other aspects. Glycomics "is the systematic study of all glycan structures of a given cell type or organism" and is a subset of glycobiology...
, analogous to genomics
Genomics
Genomics is a discipline in genetics concerning the study of the genomes of organisms. The field includes intensive efforts to determine the entire DNA sequence of organisms and fine-scale genetic mapping efforts. The field also includes studies of intragenomic phenomena such as heterosis,...
and proteomics
Proteomics
Proteomics is the large-scale study of proteins, particularly their structures and functions. Proteins are vital parts of living organisms, as they are the main components of the physiological metabolic pathways of cells. The term "proteomics" was first coined in 1997 to make an analogy with...
, is the systematic study of all glycan structures of a given cell type or organism" and is a subset of glycobiology.
Difficulties in the study of sugar structures
Part of the variability seen in saccharide structures is because monosaccharideMonosaccharide
Monosaccharides are the most basic units of biologically important carbohydrates. They are the simplest form of sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose , fructose , galactose, xylose...
units may be coupled to each other in many different ways, as opposed to the amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s of 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 or the nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
s in DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
, which are always coupled together in a standard fashion. The study of glycan structures is also complicated by the lack of a direct template for their biosynthesis, contrary to the case with proteins where their amino acid sequence is determined by their corresponding gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
.
Glycans are secondary gene products and therefore are generated by the coordinated action of many enzymes in the subcellular compartments of a cell. Since the structure of a glycan may depend on the 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...
, activity and accessibility of the different biosynthetic enzymes, it is not possible to use recombinant DNA
Recombinant DNA
Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...
technology in order to produce large quantities of glycans for structural and functional studies as it is for proteins.
Modern tools and techniques for glycan structure prediction
Accurate machines and advanced software programs, when used in combination, can unlock the mystery of glycan structures. One such technique is Mass SpectrometryMass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
which uses three principal units: the ionizer, analyzer and detector. Fast Atom Bombardment (FAB) mass spectrometers are powerful tools for characterizing complex carbohydrates. This technique can be coupled with sensitive array detector technology.
External links
- The Functional Glycomics Gateway. monthly updated web resource, a collaboration of Nature and the Consortium for Functional Glycomics.
- Carolyn Bertozzi's iBioSeminar on Chemical Glycobiology