Glycogenin

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glycogenin 1
Identifiers
Symbol	GYG1
Alt. Symbols	GYG
Entrez	2992
HUGO	4699
OMIM	603942
RefSeq	NM_004130
UniProt	P46976
Other data
Locus	Chr. 3 q24-q25.1

glycogenin 2
Identifiers
Symbol	GYG2
Entrez	8908
HUGO	4700
OMIM	300198
RefSeq	NM_003918
UniProt	O15488
Other data
Locus	Chr. X p22.3

Glycogenin is an enzyme involved in glycogen biosynthesis. This enzyme was discovered by Dr. William J. Whelan, a fellow of the Royal Society of London and current professor of Biochemistry at the University of Miami. It is a homodimer of 37-kd subunits and is classified as a glycosyltransferase.

[edit] Function

The main enzyme involved in glycogen polymerisation, glycogen synthase, can only add to an existing chain of at least 8 glucose residues. Glycogenin acts as the primer, to which further glucose monomers may be added. It achieves this by catalyzing the addition of glucose to itself (autocatalysis) by first binding glucose from UDP-glucose to the hydroxyl group of Tyr-194. Seven more glucoses can be added, each derived from UDP-glucose, by glycogenin's glucosyltransferase activity. Once sufficient residues have been added, glycogen synthase takes over extending the chain. Glycogenin remains covalently attached to the reducing end of the glycogen molecule.

evidence accumulates that a priming protein may be a fundamental property of polysaccharide synthesis in general, the molecular details of mammalian glycogen biogenesis may serve as a useful model for other systems.