Redox- and Calmodulin-dependent S-Nitrosylation of the KCNQ1 Channel

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 (I-Ks) irrespective of soluble guanylate cyclase activation. Here we demonstrate using a biotin-switch assay that NO induced S-nitrosylation of the alpha-subunit of the IKs channel, KCNQ1, at Cys(445) in the C terminus. A redox motif flanking Cys(445) and the interaction of KCNQ1 with calmodulin are required for preferential S-nitrosylation of Cys(445). A patch clamp experiment shows that S-nitrosylation of Cys(445) modulates the KCNQ1/KCNE1 channel function. Our data provide a molecular basis of NO-mediated regulation of the I-Ks channel. This novel regulatory mechanism of the I-Ks 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.