Unphosphorylated glycogen synthase 2 (GYS2-a) complexed with oligo-D-glucose-GYG2 catalyzes the polyglucosylation of the latter. (Here the addition of four glucose residues is annotated.) (Orho et al. 1998; Roach et al. 2012).

Glycogen synthase 2 (GYS2) catalyzes the incorporation of phosphoglucose into the glycogen-GYG1 molecules with which it is associated in a cytosolic glycogen granule. This reaction occurs at a low rate, yielding approximately one molecule of glucose phosphorylated at its C2, C3, or C6 positions incorporated into a growing glycogen polymer per ten thousand glucose molecules incorporated (DePaoli-Roach et al. 2015; Irimia et al. 2015; Nitschke et al. 2013; Tagliabracci et al. 2011). The function of these small amounts of phosphoglucose in normal glycogen remains to be established. This reaction has been characterized in muscle cells, where it is catalyzed by the homologous GYS1 enzyme. The occurrence of the reaction in liver, catalyzed by GYS2, can be inferred from the fact that in the absence of the enzyme EMP2A (laforin) that removes these phosphate groups, abnormally phosphorylated glycogen accumulates in both tissues (Worby et al. 2008).

Glycogen synthase 2 (GYS2) normally catalyzes the addition of glucose residues to a growing glycogen molecule. In its absence, glycogen synthesis fails. GYS2 is expressed in the liver and its deficiency is most prominently associated with fasting hypoglycemia (Gitzelmann et al. 1996). Seven human GYS2 mutations have been described, one frameshift and six missense mutations (Orho et al. 1998), Two of the missense mutations are annotated here.

Glycogenin 2 (GYG2) catalyzes its autoglycosylation reaction with UDP-glucose to form oligo (1,4)-alpha-D-glucosyl GYG2 (Mu et al. 1997). The oligosaccharide is annotated here as containing four glucose residues. Glycogenin occurs as a homodimer complexed with two molecules of glycogen synthase 1 (GYS2), here in a unphosphorylated (a) form (Roach et al. 2012).

Glycogenin 2 (GYG2) catalyzes its autoglycosylation reaction with UDP-glucose to form oligo (1,4)-alpha-D-glucosyl GYG2 (Mu et al. 1997). The oligosaccharide is annotated here as containing four glucose residues. Glycogenin occurs as a homodimer complexed with two molecules of glycogen synthase 1 (GYS2), here in a phosphorylated (b) form (Roach et al. 2012).

Glycogen synthase 2 (GYS2 "liver") normally catalyzes the addition of glucose residues to a growing glycogen molecule. In its absence, glycogen synthesis fails. Expression of GYS2 is confined to the liver and its deficiency is most prominently associated with fasting hypoglycemia (Gitzelmann et al. 1996; Orho et al. 1998).

Glycogen [starch] synthase, liver.