title: NO and CO differentially activate soluble guanylyl cyclase via a heme pivot-bend mechanism.
abstract: Diatomic ligand discrimination by soluble guanylyl cyclase (sGC) is paramount to cardiovascular homeostasis and neuronal signaling. Nitric oxide (NO) stimulates sGC activity 200-fold compared with only four-fold by carbon monoxide (CO). The molecular details of ligand discrimination and differential response to NO and CO are not well understood. These ligands are sensed by the heme domain of sGC, which belongs to the heme nitric oxide oxygen (H-NOX) domain family, also evolutionarily conserved in prokaryotes. Here we report crystal structures of the free, NO-bound, and CO-bound H-NOX domains of a cyanobacterial homolog. These structures and complementary mutational analysis in sGC reveal a molecular ruler mechanism that allows sGC to favor NO over CO while excluding oxygen, concomitant to signaling that exploits differential heme pivoting and heme bending. The heme thereby serves as a flexing wedge, allowing the N-terminal subdomain of H-NOX to shift concurrent with the transition of the six- to five-coordinated NO-bound state upon sGC activation. This transition can be modulated by mutations at sGC residues 74 and 145 and corresponding residues in the cyanobacterial H-NOX homolog.
authors.affiliation: Department of Biochemistry/RT500, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Ma
authors.forename: Nazish
authors.initials: N
authors.lastname: Sayed
authors.forename: Annie
authors.initials: A
authors.lastname: Beuve
authors.forename: Focco
authors.initials: F
authors.lastname: van den Akker
mesh_terms: D000595:Amino Acid Sequence; D017033:Anabaena / Q000201:enzymology; D000818:Animals; D019556:COS Cells; D002248:Carbon Monoxide / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D006162:Guanylate Cyclase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009569:Nitric Oxide / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D000071756:Soluble Guanylyl Cyclase; D013379:Substrate Specificity
chemical_list: D018160:Receptors, Cytoplasmic and Nuclear; D009569:Nitric Oxide; D006418:Heme; D002248:Carbon Monoxide; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase