Vibrational Analysis of Mononitrosyl Complexes in Hemerythrin and Flavodiiron Proteins: Relevance to Detoxifying NO Reductase

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• 作者：Takahiro Hayashi ; Jonathan D. Caranto ; Hirotoshi Matsumura ; Donald M. Kurtz ; Jr. ; Pierre Mo毛nne-Loccoz
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：April 18, 2012
• 年：2012
• 卷：134
• 期：15
• 页码：6878-6884
• 全文大小：438K
• 年卷期：v.134,no.15(April 18, 2012)
• ISSN：1520-5126

文摘

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 N₂O [Hayashi, T.; Caranto, J. D.; Wampler, D. A; Kurtz, D. M., Jr.; Mo毛nne-Loccoz, P. Biochemistry 2010, 49, 7040鈭?049]. 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 谓(NO) at 1658 cm^鈥?, the lowest 谓(NO) ever reported for a nonheme {FeNO}⁷ species. Both deflavo-FDP(NO) and the mononitrosyl adduct of the flavinated FPD (FDP(NO)) show 谓(NO) at 1681 cm^鈥?, 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^{鈥?/sup>) 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鈥?/sup>) 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 N₂O. This latter scenario is supported by theoretical modeling [Blomberg, L. M.; Blomberg, M. R.; Siegbahn, P. E. J. Biol. Inorg. Chem. 2007, 12, 79鈭?9]. Published vibrational data on bioengineered models of denitrifying heme-nonheme NO reductases [Hayashi, T.; Miner, K. D.; Yeung, N.; Lin, Y.-W.; Lu, Y.; Mo毛nne-Loccoz, P. Biochemistry 2011, 50, 5939鈭?947] support a similar mode of activation of a heme {FeNO}7 species by the nearby nonheme Fe(II).}