Aspartate 102 in the Heme Domain of Soluble Guanylyl Cyclase Has a Key Role in NO Activation

Nitric oxide (NO) is involved in the physiology and pathophysiology of the cardiovascular and neuronal systems via activation of soluble guanylyl cyclase (sGC), a heme-containing heterodimer. Recent structural studies have allowed a better understanding of the residues that dictate the affinity and binding of NO to the heme and the resulting breakage of the bond between the heme iron and histidine 105 (H105) of the beta subunit of sGC. Still, it is unknown how the breakage of the iron His bond translates into NO-dependent increased catalysis. Structural studies on homologous H-NOX domains in various states pointed to a role for movement of the H105 containing alpha F helix. Our modeling of the heme-binding domain highlighted conserved residues in the vicinity of H105 that could potentially regulate the extent to which the aF helix shifts and/or propagate the activation signal once the covalent bond with H105 has been broken. These include a direct interaction of alpha F helix residue aspartate 102 (D102) with the backbone nitrogen of F120. Mutational analysis of this region points to an essential role of the interactions in the vicinity of H105 for heme stability and identifies D102 as having a key role in NO activation following breakage of the iron-His bond.