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Publication Abstract from PubMed

Nitric oxide reductase (NOR) catalyzes the generation of nitrous oxide (N2 O) via the reductive coupling of two nitric oxide (NO) molecules at a heme/non-heme Fe center. We report herein on the structures of the reduced and ligand-bound forms of cytochrome c-dependent NOR (cNOR) from Pseudomonas aeruginosa at a resolution of 2.3-2.7 A, to elucidate structure-function relationships in NOR, and compare them to those of cytochrome c oxidase (CCO) that is evolutionarily related to NOR. Comprehensive crystallographic refinement of the CO-bound form of cNOR suggested that a total of four atoms can be accommodated at the binuclear center. Consistent with this, binding of bulky acetaldoxime (CH3 -CH=N-OH) to the binuclear center of cNOR was confirmed by the structural analysis. Active site reduction and ligand binding in cNOR induced only ~0.5 A increase in the heme/non-heme Fe distance, but no significant structural change in the protein. The highly localized structural change is consistent with the lack of proton-pumping activity in cNOR, because redox-coupled conformational changes are thought to be crucial for proton pumping in CCO. It also permits the rapid decomposition of cytotoxic NO in denitrification. In addition, the shorter heme/non-heme Fe distance even in the bulky ligand-bound form of cNOR (~4.5 A) than the heme/Cu distance in CCO (~5 A) suggests the ability of NOR to maintain two NO molecules within a short distance in the confined space of the active site, thereby facilitating N-N coupling to produce a hyponitrite intermediate for the generation of N2 O. (c) Proteins 2013;. (c) 2013 Wiley Periodicals, Inc.

Structures of reduced and ligand-bound nitric oxide reductase provide insights into functional differences in respiratory enzymes.,Sato N, Ishii S, Sugimoto H, Hino T, Fukumori Y, Sako Y, Shiro Y, Tosha T Proteins. 2013 Dec 13. doi: 10.1002/prot.24492. PMID:24338896^[1]

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