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Publication Abstract from PubMed

Hemoproteins play central roles in the formation and utilization of nitric oxide (NO) in cellular signalling, as well as in protection against nitrosative stress. Key to heme-nitrosyl function and reactivity is the Fe coordination number (5 or 6). For 5c-NO complexes, the potential exists for NO to bind on either heme face, as in the microbial cytochrome c' from Alcaligenes xylosoxidans (AxCYTcp), which forms a stable proximal 5c-NO complex via a distal 6c-NO intermediate and a putative dinitrosyl species. Strong parallels between the NO binding kinetics of AxCYTcp, the eukaryotic NO-sensor, soluble guanylate cyclase, and the ferrocytochrome c/cardiolipin complex have led to the suggestion that a distal to proximal NO switch could contribute to the selective ligand responses in gas-sensing hemoproteins. The proximal NO binding site in AxCYTcp is close to a conserved basic (Arg 124) residue that is postulated to modulate NO reactivity. We have replaced Arg 124 by five different amino acids and have determined high-resolution (1.07-1.40A) crystallographic structures with and without NO. These, together with kinetic and resonance Raman data, provide new insights into the mechanism of distal to proximal heme-NO conversion, including the determinants of Fe-His bond scission. The Arg124Ala variant allowed us to determine the structure of an analog of the previously unobserved key 5c-NO distal intermediate species. The very high-resolution structures combined with the extensive spectroscopic and kinetic data have allowed us to provide a fresh insight into heme reactivity towards NO, a reaction that is of wide importance in biology.

Distal to proximal NO conversion in hemoproteins: The role of the proximal pocket.,Hough MA, Antonyuk SV, Barbieri S, Rustage N, McKay AL, Servid AE, Eady RR, Andrew CR, Hasnain SS J Mol Biol. 2010 Nov 9. PMID:21073879^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.