glycans

Definition: The terms glycan and polysaccharide are defined by IUPAC as synonyms meaning "compounds consisting of a large number of monosaccharides linked glycosidically".

However, in practice the term glycan may also be used to refer to the carbohydrate portion of a glycoconjugate, such as a glycoprotein, glycolipid, or a proteoglycan, even if the carbohydrate is only an oligosaccharide.

Glycans usually consist solely of O-glycosidic linkages of monosaccharides. For example, cellulose is a glycan (or, to be more specific, a glucan) composed of β-1,4-linked D-glucose, and chitin is a glycan composed of β-1,4-linked N-acetyl-D-glucosamine. Glycans can be homo- or heteropolymers of monosaccharide residues, and can be linear or branched.

A glycan is a polysaccharide or oligosaccharide among carbohydrates. Glycan may also be used to refer to the carbohydrate portion of a glycoconjugate, such as a glycoprotein, glycolipid, or a proteoglycan.

Glycans usually consist solely of O-glycosidic linkages of monosaccharides. For example, cellulose is a glycan (or more specifically a glucan) composed of beta-1,4-linked D-glucose, and chitin is a glycan composed of beta-1,4-linked N-acetyl-D-glucosamine.

Glycans can be homo or heteropolymers of monosaccharide residues, and can be linear (linear glycans) or branched (branched glycans).

The spectrum of all glycan structures (glycome) is immense. In humans, its size is orders of magnitude greater than the number of proteins that are encoded by the genome, one percent of which encodes proteins that make, modify, localize or bind sugar chains, which are known as glycans.

Pathology

 glycan metabolism diseases

• Over 30 genetic diseases have been identified that alter glycan synthesis and structure, and ultimately the function of nearly all organ systems. Many of the causal mutations affect key biosynthetic enzymes, but more recent discoveries point to defects in chaperones and Golgi-trafficking complexes that impair several glycosylation pathways.

 glycans and cancer

• A growing body of evidence supports crucial roles for glycans at various pathophysiological steps of tumour progression. Glycans regulate tumour proliferation, invasion, haematogenous metastasis and angiogenesis, and increased understanding of these roles sets the stage for developing pharmaceutical agents that target these molecules. Such novel agents might be used alone or in combination with operative and/or chemoradiation strategies for treating cancer.

See also

 glycan metabolism

References

 Freeze HH. Genetic defects in the human glycome. Nat Rev Genet. 2006 Jul;7(7):537-51. Nat Rev Genet. 2006 Aug;7(8):660. PMID: 16755287

 Fuster MM, Esko JD. The sweet and sour of cancer: glycans as novel therapeutic targets. Nat Rev Cancer. 2005 Jul;5(7):526-42. PMID: 16069816

 Dube DH, Bertozzi CR. Glycans in cancer and inflammation - potential for therapeutics and diagnostics. Nat Rev Drug Discov. 2005 Jun;4(6):477-88. PMID: 15931257

 Kleene R, Schachner M. Glycans and neural cell interactions. Nat Rev Neurosci. 2004 Mar;5(3):195-208. PMID: 14976519