The switch helix: a putative combinatorial relay for interprotomer communication in cGMP-dependent protein kinase.

For over three decades the isozymes of cGMP-dependent protein kinase (PKG) have been studied using an array of biochemical and biophysical techniques. When compared to its closest cousin, cAMP-dependent protein kinase (PKA), these studies revealed a set of identical domain types, yet containing distinct, sequence-specific features. The recently solved structure of the PKG regulatory domain showed the presence of the switch helix (SW), a novel motif that promotes the formation of a domain-swapped dimer in the asymmetric unit. This dimer is mediated by the interaction of a knob motif on the C-terminal locus of the SW, with a hydrophobic nest on the opposing protomer. This nest sits adjacent to the cGMP binding pocket of the B-site. Priming of this site by cGMP may influence the geometry of the hydrophobic nest. Moreover, this unique interaction may have wide implications for the architecture of the inactive and active forms of PKG. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases (2012).