Journal article

Oxidant sensor in the cGMP-binding pocket of PKGI alpha regulates nitroxyl-mediated kinase activity

Despite the mechanisms for endogenous nitroxyl (HNO) production and action being incompletely understood, pharmacological donors show broad therapeutic promise and are in clinical trials. Mass spectrometry and site-directed mutagenesis showed that chemically distinct HNO donors 1-nitrosocyclohexyl acetate or Angeli's salt induced disulfides within cGMP-dependent protein kinase I-alpha (PKGI alpha), an interdisulfide between Cys42 of the two identical subunits of the kinase and a previously unobserved intradisulfide between Cys117 and Cys195 in the high affinity cGMP-binding site. Kinase activity was monitored in cells transfected with wildtype (WT), Cys42Ser or Cys117/195Ser PKGI alpha that cannot form the inter-or intradisulfide, respectively. HNO enhanced WT kinase activity, an effect significantly attenuated in inter-or intradisulfide-deficient PKGI alpha. To investigate whether the intradisulfide modulates cGMP binding, real-time imaging was performed in vascular smooth muscle cells expressing a FRET-biosensor comprising the cGMP-binding sites of PKGI alpha. HNO induced FRET changes similar to those elicited by an increase of cGMP, suggesting that intradisulfide formation is associated with activation of PKGI alpha. Intradisulfide formation in PKGI alpha correlated with enhanced HNO mediated vasorelaxation in mesenteric arteries in vitro and arteriolar dilation in vivo in mice. HNO induces intradisulfide formation in PKGIa, inducing the same effect as cGMP binding, namely kinase activation and thus vasorelaxation.


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