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Vibrational analysis of mononitrosyl complexes in hemerythrin and flavodiiron proteins: Relevance to detoxifying no reductase

Takahiro Hayashi; Jonathan D. Caranto; Hirotoshi Matsumura; Donald M. Kurtz; Pierre Moënne-Loccoz

(Profiled Author: Pierre Moenne-Loccoz)

Journal of the American Chemical Society. 2012;134(15):6878-6884.


Flavodiiron proteins (FDPs) play important roles in the microbial nitrosative stress response in low-oxygen environments by reductively scavenging nitric oxide (NO). Recently, we showed that FMN-free diferrous FDP from Thermotoga maritima exposed to 1 equiv NO forms a stable diiron-mononitrosyl complex (deflavo-FDP(NO)) that can react further with NO to form N 2O [ Hayashi, T.; Caranto, J. D.; Wampler, D. A; Kurtz, D. M., Jr.; Moënne-Loccoz, P.Biochemistry 2010, 49, 7040-7049 ]. Here we report resonance Raman and low-temperature photolysis FTIR data that better define the structure of this diiron-mononitrosyl complex. We first validate this approach using the stable diiron-mononitrosyl complex of hemerythrin, Hr(NO), for which we observe a ν(NO) at 1658 cm -1, the lowest ν(NO) ever reported for a nonheme {FeNO} 7 species. Both deflavo-FDP(NO) and the mononitrosyl adduct of the flavinated FPD (FDP(NO)) show ν(NO) at 1681 cm -1, which is also unusually low. These results indicate that, in Hr(NO) and FDP(NO), the coordinated NO is exceptionally electron rich, more closely approaching the Fe(III)(NO -) resonance structure. In the case of Hr(NO), this polarization may be promoted by steric enforcement of an unusually small FeNO angle, while in FDP(NO), the Fe(III)(NO -) structure may be due to a semibridging electrostatic interaction with the second Fe(II) ion. In Hr(NO), accessibility and steric constraints prevent further reaction of the diiron-mononitrosyl complex with NO, whereas in FDP(NO) the increased nucleophilicity of the nitrosyl group may promote attack by a second NO to produce N 2O. This latter scenario is supported by theoretical modeling [ Blomberg, L. M.; Blomberg, M. R.; Siegbahn, P. E.J. Biol. Inorg. Chem. 2007, 12, 79-89 ]. Published vibrational data on bioengineered models of denitrifying heme-nonheme NO reductases [ Hayashi, T.; Miner, K. D.; Yeung, N.; Lin, Y.-W.; Lu, Y.; Moënne-Loccoz, P.Biochemistry 2011, 50, 5939-5947 ] support a similar mode of activation of a heme {FeNO} 7 species by the nearby nonheme Fe(II). © 2012 American Chemical Society.

PMID: 22449095     PMCID: PMC3335888    

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