Arginine 75 in the pseudosubstrate sequence of type I beta cGMP-dependent protein kinase is critical for autoinhibition, although autophosphorylated serine 63 is outside this sequence

Autoinhibitory domains in many protein kinases include either a phosphorylatable substrate-like sequence or a pseudosubstrate sequence, This study shows that I beta cGMP-dependent protein kinase (cGK) autophosphorylates Ser-63, which is in an atypical cGK substrate sequence (-(59)AQKQSAS-) that is amino-terminal to the pseudosubstrate motif (-(74)KRQAI-), cGMP increases the rate of autophosphorylation (similar to 0,8 phosphate/cGK monomer) similar to 3-fold, Autophosphorylation is an intramolecular process since it is independent of cGK concentration, cGMP activation of cGK enhances proteolysis within and near the pseudosubstrate site; treatment of dimeric cGK with three proteases produces three cGK monomers (similar to 67-70 kDa each), Their amino-terminal sequences are (75)RQAISAEPT-, (76)QAlSAEPTAF-, and (86)DIQDLSXV-, respectively, cGMP stimulates these kinases by 10-, 2.5-, and 1,4-fold, respectively, compared with a 10-fold effect on intact cGK, Increased basaI activity accounts for the diminished stimulation, Thus, the primary autophosphorylation site of I beta cGK is well outside the pseudosubstrate site, but Arg-75 in the pseudosubstrate site is critical for autoinhibition, Autoinhibition also involves elements that are carboxyl-terminal to Arg-75.