How Does Single Oxygen Atom Addition Affect the Properties of an Fe-Nitrile Hydratase Analogue? The Compensatory Role of the Unmodified Thiolate
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- 作者：Priscilla Lugo-Mas ; Abhishek Dey ; Liang Xu ; Steven D. Davin ; Jason Benedict ; Werner Kaminsky ; Keith O. Hodgson ; Britt Hedman ; Edward I. Solomon ; Julie A. Kovacs
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：August 30, 2006
- 年：2006
- 卷：128
- 期：34
- 页码：11211 - 11221
- 全文大小：522K
- 年卷期：v.128,no.34(August 30, 2006)
- ISSN：1520-5126
文摘
Nitrile hydratase (NHase) is one of a growing number of enzymes shown to contain post-translationally modified cysteine sulfenic acids (Cys-SOH). Cysteine sulfenic acids have been shown toplay diverse roles in cellular processes, including transcriptional regulation, signal transduction, and theregulation of oxygen metabolism and oxidative stress responses. The function of the cysteine sulfenic acidcoordinated to the iron active site of NHase is unknown. Herein we report the first example of a sulfenate-ligated iron complex, [FeIII(ADIT)(ADIT-O)]+ (5), and compare its electronic and magnetic properties withthose of structurally related complexes in which the sulfur oxidation state and protonation state have beensystematically altered. Oxygen atom addition was found to decrease the unmodified thiolate Fe-S bondlength and blue-shift the ligand-to-metal charge-transfer band (without loss of intensity). S K-edge X-rayabsorption spectroscopy and density functional theory calculations show that, although the modified RS-O- fragment is incapable of forming a 
bond with the FeIII center, the unmodified thiolate compensates forthis loss of bonding by increasing its covalent bond strength. The redox potential shifts only slightly (75mV), and the magnetic properties are not affected (the S = 1/2 spin state is maintained). The coordinatedsulfenate S-O bond is activated and fairly polarized (S+-O-). Addition of strong acids at low temperaturesresults in the reversible protonation of sulfenate-ligated 5. An X-ray structure demonstrates that Zn2+ bindsto the sulfenate oxygen to afford [FeIII(ADIT)(ADIT-O-ZnCl3)] (6). The coordination of ZnCl3- to the RS-O-unit causes the covalent overlap with the unmodified thiolate to increase further. A possible catalytic rolefor the unmodified NHase thiolate, involving its ability to "tune" the electronics in response to protonationof the sulfenate (RS-O-) oxygen and/or substrate binding, is discussed.
bond with the FeIII center, the unmodified thiolate compensates forthis loss of bonding by increasing its covalent bond strength. The redox potential shifts only slightly (75mV), and the magnetic properties are not affected (the S = 1/2 spin state is maintained). The coordinatedsulfenate S-O bond is activated and fairly polarized (S+-O-). Addition of strong acids at low temperaturesresults in the reversible protonation of sulfenate-ligated 5. An X-ray structure demonstrates that Zn2+ bindsto the sulfenate oxygen to afford [FeIII(ADIT)(ADIT-O-ZnCl3)] (6). The coordination of ZnCl3- to the RS-O-unit causes the covalent overlap with the unmodified thiolate to increase further. A possible catalytic rolefor the unmodified NHase thiolate, involving its ability to "tune" the electronics in response to protonationof the sulfenate (RS-O-) oxygen and/or substrate binding, is discussed.