DST/NRF Centre of Excellence for Biomedical TB Research, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand and the National Health Laboratory Service, P.O. Box 1038, Johannesburg, 2000, South Africa.
MRC-CAPRISA HIV-TB Pathogenesis and Treatment Research Unit, Centre for the AIDS Programme of Research in South Africa, CAPRISA, Durban, South Africa.
Sci Rep. 2019 Mar 26;9(1):5194. doi: 10.1038/s41598-019-41001-x.
Penicillin binding proteins (PBPs) are the target of numerous antimicrobial agents that disrupt bacterial cell wall synthesis. In mycobacteria, cell elongation occurs through insertion of nascent cell wall material in the sub-polar region, a process largely driven by High Molecular Weight PBPs. In contrast, the function of DD-carboxypeptidases (DD-CPases), which are Low Molecular Weight Class 1C PBPs, in mycobacteria remains poorly understood. Mycobacterium smegmatis encodes four putative DD-CPase homologues, which display homology to counterparts in Escherichia coli. Herein, we demonstrate that these are expressed in varying abundance during growth. Deletion of MSMEG_1661, MSMEG_2433 or MSMEG_2432, individually resulted in no defects in growth, cell morphology, drug susceptibility or spatial incorporation of new peptidoglycan. In contrast, deletion of MSMEG_6113 (dacB) was only possible in a merodiploid strain expressing the homologous M. tuberculosis operon encoding Rv3627c (dacB), Rv3626c, Rv3625c (mesJ) and Rv3624c (hpt), suggestive of essentiality. To investigate the role of this operon in mycobacterial growth, we depleted gene expression using anhydrotetracycline-responsive repressors and noted reduced bipolar peptidoglycan synthesis. These data point to a possible role for this four gene operon, which is highly conserved across all mycobacterial species, in regulating spatial localization of peptidoglycan synthesis.
青霉素结合蛋白（PBPs）是许多破坏细菌细胞壁合成的抗菌药物的靶标。在分枝杆菌中，细胞的伸长是通过在亚极区插入新的细胞壁物质来实现的，这一过程主要由高分子量 PBPs 驱动。相比之下，DD-羧肽酶（DD-CPases）的功能，即低分子量 1C 类 PBPs，在分枝杆菌中的作用仍知之甚少。耻垢分枝杆菌编码四个假定的 DD-CPase 同源物，它们与大肠杆菌的对应物具有同源性。本文证明，这些蛋白在生长过程中以不同的丰度表达。单独缺失 MSMEG_1661、MSMEG_2433 或 MSMEG_2432 不会导致生长、细胞形态、药物敏感性或新肽聚糖的空间掺入缺陷。相比之下，缺失 MSMEG_6113（dacB）仅在表达同源的 M. tuberculosis 操纵子的merodiploid 菌株中是可能的，该操纵子编码 Rv3627c（dacB）、Rv3626c、Rv3625c（mesJ）和 Rv3624c（hpt），表明其是必需的。为了研究该操纵子在分枝杆菌生长中的作用，我们使用脱水四环素响应抑制剂耗尽基因表达，发现双极肽聚糖合成减少。这些数据表明，这个由四个基因组成的操纵子在调节肽聚糖合成的空间定位方面可能具有重要作用，该操纵子在所有分枝杆菌物种中高度保守。
