The mechanism behind the selection of two different cleavage sites in NAG-NAM polymers.
The mechanism behind the selection of two different cleavage sites in NAG-NAM polymers.
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DOI：
10.1107/s2052252517000367
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发表时间：
2017-03-01
期刊：
影响因子：
3.9
通讯作者：
Turk D
中科院分区：
文献类型：
--
作者：
Mihelič M;Vlahoviček-Kahlina K;Renko M;Mesnage S;Doberšek A;Taler-Verčič A;Jakas A;Turk D
自溶素E是金黄色葡萄球菌的一种N-乙酰氨基葡萄糖苷酶，它的晶体结构揭示了在NAG-NAM聚合物中连接两个化学上等价但顺序不同的β-糖苷键的壁酰胺酶和氨基葡萄糖苷酶选择机制的结构基础。肽聚糖是一种巨大的分子，它形成了包裹细菌细胞的细胞壁。它由N-乙酰氨基葡萄糖(NAG)和N-乙酰胞壁酸(NAM)残基交替组成，通过β-(1，4)-糖苷键连接，并与短的多肽链交联。由于针对肽聚糖合成的药物的抗药性日益增强，对参与肽聚糖降解的酶的研究，如N-乙酰氨基葡萄糖苷酶，可能会揭示新的有价值的药物靶点。这里讨论的科学挑战是溶菌酶、可能是有史以来研究最多的酶的溶菌酰胺酶和细菌N-乙酰氨基葡萄糖苷酶如何区分同一NAG-NAM聚合物中序列不同但化学相同的两个糖苷键。尽管对溶菌酶的结构研究已有五十多年的历史，但仍不清楚该酶是如何选择要切割的键的。利用大分子结晶学、化学合成和分子模拟，本研究解释了这两组基于相同结构核心的酶如何在选择性方面表现出差异。金黄色葡萄球菌N-乙酰氨基葡萄糖苷酶自溶素E(ATIL)的晶体结构表明，N-乙酰氨基葡萄糖苷酶和胞壁酰胺酶以交替的糖苷键位置从相反的两侧靠近底物。N-乙酰氨基葡萄糖苷酶活性部位的NAM残基的识别口袋可能使其成为合适的药物靶点。
The crystal structure of autolysin E, an N-acetylglucosaminidase from S. aureus, reveals the structural basis of the selection mechanism of muramidases and glucosaminidases for docking the two chemically equivalent, yet distinct in sequence, β-glycosidic bonds in NAG-NAM polymers. Peptidoglycan is a giant molecule that forms the cell wall that surrounds bacterial cells. It is composed of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) residues connected by β-(1,4)-glycosidic bonds and cross-linked with short polypeptide chains. Owing to the increasing antibiotic resistance against drugs targeting peptidoglycan synthesis, studies of enzymes involved in the degradation of peptidoglycan, such as N-acetylglucosaminidases, may expose new, valuable drug targets. The scientific challenge addressed here is how lysozymes, muramidases which are likely to be the most studied enzymes ever, and bacterial N-acetylglucosaminidases discriminate between two glycosidic bonds that are different in sequence yet chemically equivalent in the same NAG-NAM polymers. In spite of more than fifty years of structural studies of lysozyme, it is still not known how the enzyme selects the bond to be cleaved. Using macromolecular crystallography, chemical synthesis and molecular modelling, this study explains how these two groups of enzymes based on an equivalent structural core exhibit a difference in selectivity. The crystal structures of Staphylococcus aureus N-acetylglucosaminidase autolysin E (AtlE) alone and in complex with fragments of peptidoglycan revealed that N-acetylglucosaminidases and muramidases approach the substrate at alternate glycosidic bond positions from opposite sides. The recognition pocket for NAM residues in the active site of N-acetylglucosaminidases may make them a suitable drug target.