Insights into the Cyclic Nucleotide Selectivity Mechanism of Cyclic GMP Dependent Protein Kinase II

Abstract

Membrane bound type II cGMP dependent protein kinase (PKG II) is a central mediator of cGMP signaling cascade, which regulates circadian rhythmicity, intestinal water secretion, bone growth and renal functions. PKG II contains an N-terminal regulatory (R)-domain, and a C-terminal catalytic (C)-domain. The R-domain contains tandem cyclic nucleotide binding domains (CNB-A and B) each with different affinities for cGMP, the second messenger that regulates kinase activity of PKG II. While it is known that PKG II needs to be highly selective for cGMP over cAMP to function properly, little is known about its cyclic nucleotide selectivity and the selectivity's role in activation. To understand its cyclic nucleotide selectivity and activation mechanism of PKG II, we first identified CNB-B to be highly selective for cGMP and solved its crystal structure with cGMP. The complex structure revealed that PKG II utilizes an arginine and two aspartate residues on the C-terminal helix to recognize the guanine moiety in cGMP. This is completely different from PKG I, where a conserved arginine from the β barrel of CNB-B specifically binds the guanine moiety of cGMP and imparts cyclic nucleotide selectivity. We are currently testing the roles of PKG II specific interactions in cGMP selectivity and activation of PKG II.