Identity of the Exchangeable Sulfur-Containing Ligand at the Mo(V) Center of R160Q Human Sulfite Oxidase

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• 作者：Eric L. Klein ; Arnold M. Raitsimring ; Andrei V. Astashkin ; Asha Rajapakshe ; Kayunta Johnson-Winters ; Anna R. Arnold ; Alexey Potapov ; Daniella Goldfarb ; John H. Enemark
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：February 6, 2012
• 年：2012
• 卷：51
• 期：3
• 页码：1408-1418
• 全文大小：610K
• 年卷期：v.51,no.3(February 6, 2012)
• ISSN：1520-510X

文摘

In our previous study of the fatal R160Q mutant of human sulfite oxidase (hSO) at low pH (Astashkin et al. J. Am. Chem. Soc.2008, 130, 8471鈥?480), a new Mo(V) species, denoted 鈥渟pecies 1鈥? was observed at low pH values. Species 1 was ascribed to a six-coordinate Mo(V) center with an exchangeable terminal oxo ligand and an equatorial sulfate group on the basis of pulsed EPR spectroscopy and ³³S and ¹⁷O labeling. Here we report new results for species 1 of R160Q, based on substitution of the sulfur-containing ligand by a phosphate group, pulsed EPR spectroscopy in K_a- and W-bands, and extensive density functional theory (DFT) calculations applied to large, more realistic molecular models of the enzyme active site. The combined results unambiguously show that species 1 has an equatorial sulfite as the only exchangeable ligand. The two types of ¹⁷O signals that are observed arise from the coordinated and remote oxygen atoms of the sulfite ligand. A typical five-coordinate Mo(V) site is compatible with the observed and calculated EPR parameters.