The oxyanion hole in serine β-lactamase catalysis:: Interactions of thiono substrates with the active site
The oxyanion hole in serine β-lactamase catalysis:: Interactions of thiono substrates with the active site
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DOI：
10.1006/bioo.2000.1184
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发表时间：
2000-12-01
影响因子：
5.1
通讯作者：
Pratt, RF
中科院分区：
文献类型：
--
作者：
Curley, K;Pratt, RF
丝氨酸β-内酰胺酶的结构和功能研究表明，在酶的活性中心存在一个氧阴离子空穴，在催化中起重要作用。氧阴离子空穴的功能性存在由先前的观察结果证明，即硫代-β-内酰胺是β-内酰胺酶的非常差的底物（B. P. Murphy和R. E Pratt，1988，Biochem.J.256，669-672），并且在本论文中是由于这些酶不能催化缩肽底物的硫羰基类似物的水解。这种硫羰基效应首先在经典的丝氨酸水解酶中被注意到并解释，尽管其化学基础在这些酶或β-内酰胺酶中还没有被牢固地建立。在本文中的计算方法，以进一步了解的效果已经采取。C类β-内酰胺酶的结果表明，脱酰四面体中间体与氧阴离子孔中的O-比S-更强地相互作用。而酰化四面体中间体则匡威，这与实验结果明显不符合雅阁。这些结果表明，硫羰效应不是由酶和硫羰底物在四面体中间阶段的不利相互作用引起的，而是本质上必须是纯动力学的，即，在酰化反应的早期阶段以过渡物种出现。对A类β-内酰胺酶和胰凝乳蛋白酶的一系列不太广泛的计算也表明了关于硫代效应起源的相同结论，（C）2000 AcademicPress.
Both functional and structural studies of serine beta -lactamases indicate the existence of an oxyanion hole at the active site with an important role in catalysis. The functional presence of the oxyanion hole is demonstrated by the previous observation that thiono-beta -lactams are very poor substrates of beta -lactamases (B. P. Murphy, and R. E Pratt, 1988, Biochem. J. 256, 669-672) and in the present paper by the inability of these enzymes to catalyze hydrolysis of a thiono analog of a depsipeptide substrate. This thiono effect was first noted and interpreted in regard to classical serine hydrolases although the chemical basis for it has not been firmly established either in those enzymes or in beta -lactamases. In this paper a computational approach to a further understanding of the effect has been taken. The results for a class C beta -lactamase show that the deacylation tetrahedral intermediate interacted more strongly with the enzyme with an O- placed in the oxyanion hole than an S-. On the other hand, the converse was true for acylation tetrahedral intermediate species, a result distinctly not in accord with experiment. These results indicate that the thiono effect does not arise from unfavorable interactions between enzyme and thiono substrate at the tetrahedral intermediate stage but must be purely kinetic in nature, i.e., arise in a transitional species at an early stage of the acylation reaction. The same conclusion as to the origin of the thiono effect was also indicated by a less extensive series of calculations on a class A beta -lactamase and on chymotrypsin, (C) 2000 Academic Press.