Identification of a conserved residue responsible for the autoinhibition of cGMP-dependent protein kinase Iα and β

We isolated a constitutively active form of cGMP-dependent protein kinase I alpha (cGK I alpha) by PCR-driven random mutagenesis. The replacement of Ile-63 by Thr in the autoinhibitory domain results in the enhancement of autophosphorylation and the basal kinase activity in the absence of cGMP. The hydrophobicity at position 63 is essential for the inactive state of cGK I alpha, and Ile-78 of cGK I beta is also required for the autoinhibitory property. Furthermore, cGK I alpha (Ile-63-Thr) is constitutively active in vivo. These findings suggest that a conserved residue in the autoinhibitory domain was involved in the autoinhibition of both cGK Is. (C) 2000 Federation of European Biochemical Societies.