Shokhen Michael, Albeck Amnon
The Julius Spokojny Bioorganic Chemistry Laboratory, Department of Chemistry, Bar-Ilan University, Ramat Gan, Israel.
Proteins. 2004 Feb 15;54(3):468-77. doi: 10.1002/prot.10610.
The transformation of a weak hydrogen bond in the free enzyme into a low-barrier hydrogen bond (LBHB) in the tetrahedral intermediate has been suggested as an important factor facilitating catalysis in serine proteases. In this work, we examine the structure of the H-bond in the Asp102-His57 diad of serine proteases in the free enzyme and in a covalent tetrahedral complex (TC) with a trifluoromethylketone inhibitor. We apply ab initio quantum mechanical calculations to models consisting of a large molecular fragment of the enzyme active site, and the combined effect of the rest of the protein body and the solvation by surrounding bulk water was simulated by a self-consistent reaction field method in our novel QM/SCRF(VS) approach. Potential profiles of adiabatic proton transfer in the Asp102-His57 diad in these model systems were calculated. We conclude that the hydrogen bond in both the free enzyme and in the enzyme-inhibitor TC is a strong ionic asymmetric one-well hydrogen bond, in contrast to a previous suggestion that it is a weak H-bond in the former and a double-well LBHB in the latter.
自由酶中弱氢键向四面体中间体中的低势垒氢键（LBHB）的转变被认为是促进丝氨酸蛋白酶催化的一个重要因素。在这项工作中，我们研究了自由酶以及与三氟甲基酮抑制剂形成的共价四面体复合物（TC）中丝氨酸蛋白酶Asp102-His57二元组中氢键的结构。我们对由酶活性位点的大分子片段组成的模型应用从头算量子力学计算，并通过我们新颖的QM/SCRF(VS)方法中的自洽反应场方法模拟了蛋白质主体其余部分和周围大量水溶剂化的综合效应。计算了这些模型系统中Asp102-His57二元组中绝热质子转移的势能分布。我们得出结论，自由酶和酶-抑制剂TC中的氢键都是强离子不对称单阱氢键，这与之前认为前者是弱氢键而后者是双阱LBHB的观点相反。
