Redox- and calmodulin-dependent S-nitrosylation of the KCNQ1 channel

Abstract

Nitric oxide (NO) is a gaseous signal mediator showing numerous important biological effects. NO has been shown in many instances to exhibit its action via the protein S-nitrosylation mechanism, in which binding of NO to Cys residues regulate protein function independently of activation of soluble guanylate cyclase. The direct link between protein S-nitrosylation and functional modulation, however, has been demonstrated only in limited examples. Furthermore, although most proteins have more than one Cys residue, the mechanism by which a certain Cys becomes a specific target residue of S-nitrosylation is poorly understood. We have previously reported that NO regulates currents through the cardiac slowly activating delayed rectifier potassium channel (IKs) irrespective of soluble guanylate cyclase activation. Here we demonstrate using a biotinswitch assay that NO induced S-nitrosylation of the α-subunit of the IKs channel, KCNQ1, at Cys445 in the C terminus. A redox motif flanking Cys445 and the interaction of KCNQ1 with calmodulin are required for preferential S-nitrosylation of Cys445. A patch clamp experiment shows that S-nitrosylation of Cys445 modulates the KCNQ1/KCNE1 channel function. Our data provide a molecular basis of NO-mediated regulation of the IKs channel. This novel regulatory mechanism of the IKs channel may play a role in previously demonstrated NO-mediated phenomenon in cardiac electrophysiology, including shortening in action potential duration in response to intracellular Ca2+ or sex hormones. © 2009 by The American Society for Biochemistry and Molecular Biology, Inc.