Heme-assisted S-Nitrosation Desensitizes Ferric Soluble Guanylate Cyclase to Nitric Oxide

Nitric oxide (NO) signaling regulates key processes in cardiovascular physiology, specifically vasodilation, platelet aggregation, and leukocyte rolling. Soluble guanylate cyclase (sGC), the mammalian NO sensor, transduces an NO signal into the classical second messenger cyclic GMP (cGMP). NO binds to the ferrous (Fe2+) oxidation state of the sGC heme cofactor and stimulates formation of cGMP several hundred-fold. Oxidation of the sGC heme to the ferric (Fe3+) state desensitizes the enzyme to NO. The heme-oxidized state of sGC has emerged as a potential therapeutic target in the treatment of cardiovascular disease. Here, we investigate the molecular mechanism of NO desensitization and find that sGC undergoes a reductive nitrosylation reaction that is coupled to the S-nitrosation of sGC cysteines. We further characterize the kinetics of NO desensitization and find that heme-assisted nitrosothiol formation of β1Cys-78 and β1Cys-122 causes the NO desensitization of ferric sGC. Finally, we provide evidence that the mechanism of reductive nitrosylation is gated by a conformational change of the protein. These results yield insights into the function and dysfunction of sGC in cardiovascular disease. Background: Oxidation of the sGC heme iron causes dysfunction in NO/cGMP signal transduction, a key pathway in cardiovascular physiology. Results: NO treatment of heme-oxidized sGC restores the reduced heme state but concomitantly oxidizes β1Cys-78 and β1Cys-122. Conclusion: Heme-assisted S-nitrosation causes the NO desensitization of ferric sGC. Significance: This mechanism describes a specific role for protein thiol modification in cardiovascular disease.