Crystal structure of the S-nitroso form of liganded human hemoglobin

Although numerous reports have documented that the S-nitrosylation of cyste ine residues by NO alters the activities of a wide variety of proteins, the direct visualization and the structural consequences of this reversible mo dification have not yet been reported for any protein. Here we describe the crystal structure of S-nitroso-nitrosylhemoglobin determined at a resoluti on of 1.8 Angstrom. The specific reaction of NO with Cys93 beta is confirme d in this structure, and a large S-nitrosylation-induced change in the tert iary structure of the COOH-terminal dipeptides of the beta subunits provide s additional insight into the stereochemical mechanism by which blood flow is regulated by the interaction of NO with hemoglobin.