GSK-3 is a serine/threonine protein kinase that phosphorylate either threonine or serine, and this phosphorylation controls a variety of biological activities, such as glycogen metabolism, cell signaling, cellular transport, and others.[6] GS inhibition by GSK-3β leads to a decrease in glycogen synthesis in the liver and muscles, along with increased blood glucose or hyperglycemia.[7] This is why GSK-3β is associated with the pathogenesis and progression of many diseases, such as diabetes, obesity, cancer,[8] and Alzheimer's disease.[9] It is active in resting cells and is inhibited by several hormones such as insulin, endothelial growth factor, and platelet-derived growth factor. Insulin indirectly inactivates GSK3 via downstream phosphorylation of the specific serine residues Ser21 and Ser9 in GSK-3 isoforms α and β, respectively via the PI3K/Akt pathway.[10][11]
As of 2019[update], GSK-3 is the only type of glycogen synthase kinase named and recognized. The gene symbols for GSK1 and GSK2 have been withdrawn by the HUGO Gene Nomenclature Committee (HGNC), and no new names for these "genes" nor their locations have been specified.[12][13]
^PDB: 1J1B; Aoki M, Yokota T, Sugiura I, Sasaki C, Hasegawa T, Okumura C, et al. (March 2004). "Structural insight into nucleotide recognition in tau-protein kinase I/glycogen synthase kinase 3 beta". Acta Crystallographica. Section D, Biological Crystallography. 60 (Pt 3): 439–446. Bibcode:2004AcCrD..60..439A. doi:10.1107/S090744490302938X. PMID14993667.
^Jope RS, Johnson GV (February 2004). "The glamour and gloom of glycogen synthase kinase-3". Trends in Biochemical Sciences. 29 (2): 95–102. doi:10.1016/j.tibs.2003.12.004. PMID15102436.