GSK-3

glycogen synthase kinase 3 beta
Crystallographic structure of human GSK-3β (rainbow colored, N-terminus = blue, C-terminus = red) bound to phosphoaminophosphonic acid-adenylate ester (spheres).
Identifiers
Symbol	GSK3B
Entrez	2932
HUGO	4617
OMIM	605004
PDB	1Q3W More structures
RefSeq	NM_002093
UniProt	P49841
Other data
EC number	2.7.11.26
Locus	Chr. 3 q13.33

Glycogen synthase kinase 3 is a serine/threonine protein kinase that mediates the addition of phosphate molecules onto serine and threonine amino acid residues. First discovered in 1980 as a regulatory kinase for its namesake, Glycogen synthase, GSK-3 has since been identified as a kinase for over forty different proteins in a variety of different pathways. In mammals GSK-3 is encoded by two known genes, GSK-3 alpha (GSK3A) and GSK-3 beta (GSK3B). GSK-3 has recently been the subject of much research because it has been implicated in a number of diseases, including Type II diabetes (Diabetes mellitus type 2), Alzheimer's Disease, inflammation, cancer, and bipolar disorder.

GSK-3 functions by phosphorylating a serine or threonine residue on its target substrate. A positively charged pocket adjacent to the active site binds a "priming" phosphate group attached to a serine or threonine four residues C-terminal of the target phosphorylation site. The active site, at residues 181, 200, 97, and 85, binds the terminal phosphate of ATP and transfers it to the target location on the substrate (see figure 1).

Phosphorylation of a protein by GSK-3 usually inhibits the activity of its downstream target. GSK-3 is active in a number of central intracellular signaling pathways, including cellular proliferation, migration, glucose regulation, and apoptosis.

GSK-3 was originally discovered in the context of its involvement in regulating glycogen synthase. After being primed by casein kinase 2 (CK2), glycogen synthase gets phosphorylated at a cluster of three C-terminal serine residues, reducing its activity. In addition to its role in regulating glycogen synthase, GSK-3 has been implicated in other aspects of glucose homeostasis, including the phosphorylation of insulin receptor IRS1 and of the gluconeogenic enzymes phosphoenolpyruvate carboxykinase and glucose 6 phosphatase. However, these interactions have not been confirmed, as these pathways can be inhibited without the up-regulation of GSK-3.