title: Unprecedented proximal binding of nitric oxide to heme: implications for guanylate cyclase.
abstract: Microbial cytochromes c' contain a 5-coordinate His-ligated heme that forms stable adducts with nitric oxide (NO) and carbon monoxide (CO), but not with dioxygen. We report the 1.95 and 1.35 A resolution crystal structures of the CO- and NO-bound forms of the reduced protein from Alcaligenes xylosoxidans. NO disrupts the His-Fe bond and binds in a novel mode to the proximal face of the heme, giving a 5-coordinate species. In contrast, CO binds 6-coordinate on the distal side. A second CO molecule, not bound to the heme, is located in the proximal pocket. Since the unusual spectroscopic properties of cytochromes c' are shared by soluble guanylate cyclase (sGC), our findings have potential implications for the activation of sGC induced by the binding of NO or CO to the heme domain.
authors.affiliation: Department of Biological Chemistry, John Innes Centre, Norwich, NR4 7UH, UK. david.lawson@bbsrc.ac.uk
authors.forename: D M
authors.initials: DM
authors.lastname: Lawson
authors.forename: C E
authors.initials: CE
authors.lastname: Stevenson
authors.forename: C R
authors.initials: CR
authors.lastname: Andrew
authors.forename: R R
authors.initials: RR
authors.lastname: Eady
mesh_terms: D000421:Alcaligenes / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002248:Carbon Monoxide / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry / Q000378:metabolism; D006162:Guanylate Cyclase / Q000737:chemistry / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006420:Hemeproteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D009569:Nitric Oxide / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D011487:Protein Conformation; D055672:Static Electricity; D015534:Trans-Activators / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C108776:CooA protein, Rhodospirillum rubrum; D003574:Cytochrome c Group; D006420:Hemeproteins; D015534:Trans-Activators; D009569:Nitric Oxide; D006418:Heme; D002248:Carbon Monoxide; D006162:Guanylate Cyclase