Lovering Andrew L, De Castro Liza, Lim Daniel, Strynadka Natalie C J
Department of Biochemistry and Molecular Biology, Center for Blood Research, University of British Columbia, Vancouver, Canada.
Protein Sci. 2006 Jul;15(7):1701-9. doi: 10.1110/ps.062112106. Epub 2006 Jun 2.
The class A PBP1b from Streptococcus pneumoniae is responsible for glycosyltransferase and transpeptidase (TP) reactions, forming the peptidoglycan of the bacterial cell wall. The enzyme has been produced in a stable, soluble form and undergoes time-dependent proteolysis to leave an intact TP domain. Crystals of this TP domain were obtained, diffracting to 2.2 A resolution, and the structure was solved by using molecular replacement. Analysis of the structure revealed an "open" active site, with important conformational differences to the previously determined "closed" apoenzyme. The active-site nucleophile, Ser460, is in an orientation that allows for acylation by beta-lactams. Consistent with the productive conformation of the conserved active-site catalytic residues, adjacent loops show only minor deviation from those of known acyl-enzyme structures. These findings are discussed in the context of enzyme functionality and the possible conformational sampling of PBP1b between active and inactive states.
肺炎链球菌的A类青霉素结合蛋白1b（PBP1b）负责糖基转移酶和转肽酶（TP）反应，形成细菌细胞壁的肽聚糖。该酶已以稳定的可溶形式产生，并经历时间依赖性蛋白水解，留下完整的TP结构域。获得了该TP结构域的晶体，衍射分辨率达到2.2埃，并通过分子置换解析了其结构。结构分析揭示了一个“开放”的活性位点，与先前确定的“封闭”无酶形式存在重要的构象差异。活性位点亲核试剂Ser460的取向允许被β-内酰胺酰化。与保守的活性位点催化残基的有效构象一致，相邻环与已知酰基酶结构的环仅显示出微小偏差。这些发现将在酶功能以及PBP1b在活性和非活性状态之间可能的构象采样的背景下进行讨论。
