Fig. 4.

Working model of PKGI. PKGI isozymes are homodimers that are dimerized by an extended leucine zipper region (ZZZZZ). Unique faces of the zipper regions that provide for selective homodimerization of PKGIα and PKGIβ and their selective interaction with specific cellular proteins are indicated by the combined asterisks and plus symbols (* + * +). Multiple sites of autophosphorylation are indicated by encircled P and multiple autoinhibitory contacts are indicated by dashed lines (- - - - -). The cGMP-binding sites are homologous, but the more amino-terminal site has higher affinity for cGMP, indicated by the heavy dark semicircle.