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Catalytic domain of the Serine/Threonine Kinase, cGMP-dependent protein kinase (cGK or PKG) STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. Mammals have two cGK isoforms from different genes, cGKI and cGKII. cGKI exists as two splice variants, cGKI-alpha and cGKI-beta. cGK consists of an N-terminal regulatory domain containing a dimerization and an autoinhibitory pseudosubstrate region, two cGMP-binding domains, and a C-terminal catalytic domain. Binding of cGMP to both binding sites releases the inhibition of the catalytic center by the pseudosubstrate region, allowing autophosphorylation and activation of the kinase. cGKI is a soluble protein expressed in all smooth muscles, platelets, cerebellum, and kidney. It is also expressed at lower concentrations in other tissues. cGKII is a membrane-bound protein that is most abundantly expressed in the intestine. It is also present in the brain nuclei, adrenal cortex, kidney, lung, and prostate. cGKI is involved in the regulation of smooth muscle tone, smooth cell proliferation, and platelet activation. cGKII plays a role in the regulation of secretion, such as renin secretion by the kidney and aldosterone secretion by the adrenal. It also regulates bone growth and the circadian rhythm. The cGK subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase. |
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