Structural Basis for the Interconversion of Maltodextrins by MalQ, the Amylomaltase of Escherichia coli*
Structural Basis for the Interconversion of Maltodextrins by MalQ, the Amylomaltase of Escherichia coli*
复制标题
DOI：
10.1074/jbc.m115.667337
复制
发表时间：
2015-07
期刊：
影响因子：
--
通讯作者：
S. Weiss;A. Skerra;A. Schiefner
中科院分区：
文献类型：
--
作者：
S. Weiss;A. Skerra;A. Schiefner
背景：麦芽糖淀粉酶MalQ在大肠杆菌中催化麦芽糖和麦芽糊精的转糖基化。杆菌结果：确定了三种不同的X射线结构和不同底物的产物平衡浓度。结论：MalQ在催化过程中发生了主要的构象变化，其产物谱取决于底物链长。意义：对MalQ机制及其在大肠杆菌麦芽糖代谢中的关键作用的新见解。大肠杆菌。麦芽糖淀粉酶MalQ是大肠杆菌中麦芽糖和麦芽糖糊精代谢所必需的。它催化糖基转移/糖基化反应，其中糖基或糊精基单元在各种长度的线性麦芽糖糊精之间转移。为了阐明MalQ转糖基化的分子基础，我们已经确定了这种酶的三种晶体结构，即apo形式，其与麦芽糖的复合物，以及与过渡态类似物阿卡维辛-葡萄糖-阿卡波糖的抑制剂复合物，分辨率低至2.1 μ m。MalQ代表具有已知结构的嗜温细菌淀粉麦芽糖酶的第一个实例，并且与先前描述的嗜热酶相比，其显示出约140个残基的N-末端延伸。该部分似乎是肠杆菌科的淀粉麦芽糖酶所特有的，并折叠成与催化核心的不同部分相关的两个不同的亚结构域。有趣的是，三个MalQ晶体结构似乎对应于这种酶的不同状态，揭示了催化循环过程中相当大的构象变化。特别地，抑制剂复合物强调了在受体亚位点+1处的3-OH基团和4-OH基团（或α1-4-糖苷键）对于酸/碱催化剂Glu-496的催化活性取向的需要。使用基于HPLC的MalQ酶测定，我们可以证明麦芽糊精产物的平衡浓度取决于初始底物的长度;随着糖苷键数量的增加，形成的葡萄糖减少。因此，结构和酶数据都与观察到的淀粉麦芽糖酶的极低水解速率一致，并强调了MalQ对E.杆菌
Background: Amylomaltase MalQ catalyzes the transglycosylation of maltose and maltodextrins in E. coli. Results: Three different x-ray structures and the product equilibrium concentrations for different substrates were determined. Conclusion: MalQ undergoes major conformational changes during catalysis, and its product spectrum depends on substrate chain length. Significance: Novel insights into the MalQ mechanism and its key role for maltose metabolism in E. coli were obtained. Amylomaltase MalQ is essential for the metabolism of maltose and maltodextrins in Escherichia coli. It catalyzes transglycosylation/disproportionation reactions in which glycosyl or dextrinyl units are transferred among linear maltodextrins of various lengths. To elucidate the molecular basis of transglycosylation by MalQ, we have determined three crystal structures of this enzyme, i.e. the apo-form, its complex with maltose, and an inhibitor complex with the transition state analog acarviosine-glucose-acarbose, at resolutions down to 2.1 Å. MalQ represents the first example of a mesophilic bacterial amylomaltase with known structure and exhibits an N-terminal extension of about 140 residues, in contrast with previously described thermophilic enzymes. This moiety seems unique to amylomaltases from Enterobacteriaceae and folds into two distinct subdomains that associate with different parts of the catalytic core. Intriguingly, the three MalQ crystal structures appear to correspond to distinct states of this enzyme, revealing considerable conformational changes during the catalytic cycle. In particular, the inhibitor complex highlights the requirement of both a 3-OH group and a 4-OH group (or α1–4-glycosidic bond) at the acceptor subsite +1 for the catalytically competent orientation of the acid/base catalyst Glu-496. Using an HPLC-based MalQ enzyme assay, we could demonstrate that the equilibrium concentration of maltodextrin products depends on the length of the initial substrate; with increasing numbers of glycosidic bonds, less glucose is formed. Thus, both structural and enzymatic data are consistent with the extremely low hydrolysis rates observed for amylomaltases and underline the importance of MalQ for the metabolism of maltodextrins in E. coli.