Water Promoting Electron Hole Transport between Tyrosine and Cysteine in Proteins via a Special Mechanism: Double Proton Coupled Electron Transfer

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• 作者：Xiaohua Chen ; Guangcai Ma ; Weichao Sun ; Hongjing Dai ; Dong Xiao ; Yanfang Zhang ; Xin Qin ; Yongjun Liu ; Yuxiang Bu
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：March 26, 2014
• 年：2014
• 卷：136
• 期：12
• 页码：4515-4524
• 全文大小：575K
• 年卷期：v.136,no.12(March 26, 2014)
• ISSN：1520-5126

文摘

The proton/electron transfer reactions between cysteine residue (Cys) and tyrosinyl radical (Tyr^{鈥?/sup>) are an important step for many enzyme-catalyzed processes. On the basis of the statistical analysis of protein data bank, we designed three representative models to explore the possible proton/electron transfer mechanisms from Cys to Tyr鈥?/sup> in proteins. Our ab initio calculations on simplified models and quantum mechanical/molecular mechanical (QM/MM) calculations on real protein environment reveal that the direct electron transfer between Cys and Tyr鈥?/sup> is difficult to occur, but an inserted water molecule can greatly promote the proton/electron transfer reactions by a double-proton-coupled electron transfer (dPCET) mechanism. The inserted H₂O plays two assistant roles in these reactions. The first one is to bridge the side chains of Tyr鈥?/sup> and Cys via two hydrogen bonds, which act as the proton pathway, and the other one is to enhance the electron overlap between the lone-pair orbital of sulfur atom and the 蟺-orbital of phenol moiety and to function as electron transfer pathway. This water-mediated dPCET mechanism may offer great help to understand the detailed electron transfer processes between Tyr and Cys residues in proteins, such as the electron transfer from Cys₄₃₉ to Tyr₇₃₀鈥?/sup> in the class I ribonucleotide reductase.}