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Cleavage of Braun’s lipoprotein Lpp from the bacterial peptidoglycan by a paralog of l,d-transpeptidases, LdtF [Biochemistry]
Proceedings of the National Academy of Sciences of the United States of America ( IF 9.412 ) Pub Date : 2021-05-11 , DOI: 10.1073/pnas.2101989118
Raj Bahadur, Pavan Kumar Chodisetti, Manjula Reddy

The gram‐negative bacterial cell envelope is made up of an outer membrane (OM), an inner membrane (IM) that surrounds the cytoplasm, and a periplasmic space between the two membranes containing peptidoglycan (PG or murein). PG is an elastic polymer that forms a mesh-like sacculus around the IM, protecting cells from turgor and environmental stress conditions. In several bacteria, including Escherichia coli, the OM is tethered to PG by an abundant OM lipoprotein, Lpp (or Braun’s lipoprotein), that functions to maintain the structural and functional integrity of the cell envelope. Since its discovery, Lpp has been studied extensively, and although l,d-transpeptidases, the enzymes that catalyze the formation of PG−Lpp linkages, have been earlier identified, it is not known how these linkages are modulated. Here, using genetic and biochemical approaches, we show that LdtF (formerly yafK), a newly identified paralog of l,d-transpeptidases in E. coli, is a murein hydrolytic enzyme that catalyzes cleavage of Lpp from the PG sacculus. LdtF also exhibits glycine-specific carboxypeptidase activity on muropeptides containing a terminal glycine residue. LdtF was earlier presumed to be an l,d-transpeptidase; however, our results show that it is indeed an l,d-endopeptidase that hydrolyzes the products generated by the l,d-transpeptidases. To summarize, this study describes the discovery of a murein endopeptidase with a hitherto unknown catalytic specificity that removes the PG−Lpp cross-links, suggesting a role for LdtF in the regulation of PG–OM linkages to maintain the structural integrity of the bacterial cell envelope.



中文翻译:

通过l,d-转肽酶LdtF的旁系同源物从细菌肽聚糖上裂解布劳恩脂蛋白Lpp [生化]

革兰氏阴性细菌细胞包膜由外膜(OM),包围细胞质的内膜(IM)和包含肽聚糖(PG或murein)的两个膜之间的周质空间组成。PG是一种弹性聚合物,可在IM周围形成网眼状的囊,保护细胞免受膨胀和环境压力的影响。在包括大肠杆菌在内的几种细菌,OM通过丰富的OM脂蛋白Lpp(或布劳恩氏脂蛋白)与PG拴系在一起,脂蛋白的功能是维持细胞包膜的结构和功能完整性。自从发现以来,Lpp已经得到了广泛的研究,尽管ld-transpeptidases,催化PG-Lpp键形成的酶,已经被较早鉴定,尚不知道如何调节这些键。在这里,用遗传和生化方法,我们表明,LdtF(以前yafK)的新鉴定的旁系同源d -transpeptidases在大肠杆菌,是胞壁质水解酶,其催化LPP的从PG球囊裂解。LdtF还对含有末端甘氨酸残基的多肽表现出甘氨酸特异性羧肽酶活性。先前认为LdtF是ld-转肽酶。但是,我们的结果表明它确实是ld-endopeptidase水解由所产生的产品d -transpeptidases。总而言之,这项研究描述了一种具有迄今未知的催化特异性的壁蛋白内肽酶的发现,该酶特异性去除了PG-Lpp交联,暗示了LdtF在调节PG-OM连锁中保持细菌细胞结构完整性的作用。信封。

更新日期:2021-05-03
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