糖基转移酶的催化和酰基转移酶模块的细胞壁peptidoglycan-polymerizing penicillin-binding蛋白质1 b的大肠杆菌。
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Terrak M, Ghosh TK,范Heijenoort J, van Beeumen J, Lampilas M, Aszodi J, Ayala是的,Ghuysen JM, Nguyen-Disteche M
糖基转移酶的催化和酰基转移酶模块的细胞壁peptidoglycan-polymerizing penicillin-binding蛋白质1 b的大肠杆菌。
摩尔Microbiol。1999年10月,34 (2):350 - 64。
- PubMed ID
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10564478 (在PubMed]
- 文摘
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penicillin-binding蛋白(PBP) 1 b的大肠杆菌催化作用组装lipid-transported n -乙酰glucosaminyl-beta-1, 4-N-acetylmuramoyl-L-alanyl-gamma-D-glutamyl - (L) -meso-diaminopimelyl + + + - (L) -D-alanyl-D-alanine二糖五肽单位聚合肽聚糖。这些单位是磷酸二酯的联系,在胞壁酸C1, C55 undecaprenyl母舰。PBP1b已净化的形式标记(M46-N844) PBP1bgamma。这个导数为宿主细胞的产生提供了一个功能肽聚糖。他的标签(M46-N844) PBP1bgamma拥有伴疏水段,是跨膜本机PBP的扳手。这段有关,通过一个等同于100 -氨基酸插入、一个D198-G435糖基转移酶模块具有五个图案的特点是类a在体外实验中,PBP糖基转移酶的催化作用的线性多糖链的合成脂质载体的效率与39 000 m - 1 s - 1。主题1,glu - 233是催化反应的中心。提出,glu - 233 gamma-COOH捐赠其质子的氧原子易裂开的phosphoester债券的脂质载体,形成oxocarbonium阳离子,然后进行攻击的哦亲核试剂N-acetylglucosamine集团。asp - 234的主题1或glu - 290的主题3可以参与oxocarbonium阳离子的稳定和激活N-acetylglucosamine哦组的。反过来,酪氨酸- 310的主题4是氨基酸sequence-folding信息的一个重要组成部分。 The glycosyl transferase module of PBP1b, the lysozymes and the lytic transglycosylase Slt70 have much the same catalytic machinery. They might be members of the same superfamily. The glycosyl transferase module is linked, via a short junction site, to the amino end of a Q447-N844 acyl transferase module, which possesses the catalytic centre-defining motifs of the penicilloyl serine transferases superfamily. In in vitro assays with the lipid precursor and in the presence of penicillin at concentrations sufficient to derivatize the active-site serine 510 of the acyl transferase, the rate of glycan chain synthesis is unmodified, showing that the functioning of the glycosyl transferase is acyl transferase independent. In the absence of penicillin, the products of the Ser-510-assisted double-proton shuttle are glycan strands substituted by cross-linked tetrapeptide-pentapeptide and tetrapeptide-tetrapeptide dimers and uncross-linked pentapeptide and tetrapeptide monomers. The acyl transferase of the PBP also catalyses aminolysis and hydrolysis of properly structured thiolesters, but it lacks activity on D-alanyl-D-alanine-terminated peptides. This substrate specificity suggests that carbonyl donor activity requires the attachment of the pentapeptides to the glycan chains made by the glycosyl transferase, and it implies that one and the same PBP molecule catalyses transglycosylation and peptide cross-linking in a sequential manner. Attempts to produce truncated forms of the PBP lead to the conclusion that the multimodular polypeptide chain behaves as an integrated folding entity during PBP1b biogenesis.