College of Biotechnology and Bioengineering, Zhejiang University of Technology, 18 Chaowang Road, Hangzhou 310014, Zhejiang Province, China.
College of Life sciences, Zhejiang University, 866 Yuhangtang Road, Hangzhou 310058, Zhejiang Province, China.
FEMS Microbiol Lett. 2020 Feb 1;367(3). doi: 10.1093/femsle/fnaa026.
In rod-shaped Gram-negative bacteria, penicillin binding protein 1a (PBP1a) and 1b (PBP1b) form peptidoglycan-synthesizing complexes with the outer membrane lipoprotein LpoA and LpoB, respectively. Escherichia coli mutants lacking PBP1b/LpoB are sicker than those lacking PBP1a/LpoA. However, we previously found that mutants lacking PBP1a/LpoA but not PBP1b/LpoB are deleterious in Shewanella oneidensis. Here, we show that S. oneidensis PBP1a (SoPBP1a) contains conserved signature motifs with its E. coli counterpart, EcPBP1a. Although EcPBP1a play a less prominent role in E. coli, it is capable of substituting for the SoPBP1a in a manner dependent on SoLpoA. In S. oneidensis, expression of PBP1b is lower than PBP1a, and therefore the additional expression of SoPBP1b at low levels can functionally compensate for the absence of SoPBP1a. Importantly, S. oneidensis PBP1a variants lacking either glycosyltransferase (GTase) or transpeptidase (TPase) activity fail to maintain normal morphology and cell envelope integrity. Similarly, SoPBP1b variants also fail to compensate for the loss of SoPBP1a. Furthermore, overproduction of variants of SoPBP1a, but not SoPBP1b, has detrimental effects on cell morphology in S. oneidensis wild type cells. Overall, our results indicate that the combined enzymatic activities of SoPBP1a are essential for cell wall homeostasis.
在杆状革兰氏阴性菌中，青霉素结合蛋白 1a（PBP1a）和 1b（PBP1b）分别与外膜脂蛋白 LpoA 和 LpoB 形成肽聚糖合成复合物。缺乏 PBP1b/LpoB 的大肠杆菌突变体比缺乏 PBP1a/LpoA 的突变体更易患病。然而，我们之前发现，缺乏 PBP1a/LpoA 但不缺乏 PBP1b/LpoB 的突变体在希瓦氏菌属（Shewanella）oneidensis 中是有害的。在这里，我们表明，希瓦氏菌属 oneidensis 的 PBP1a（SoPBP1a）含有与其大肠杆菌对应物 EcPBP1a 相同的保守特征基序。尽管 EcPBP1a 在大肠杆菌中作用不那么突出，但它能够以依赖于 SoLpoA 的方式替代 SoPBP1a。在希瓦氏菌属 oneidensis 中，PBP1b 的表达水平低于 PBP1a，因此低水平表达的额外的 SoPBP1b 可以在功能上补偿 SoPBP1a 的缺失。重要的是，缺乏糖基转移酶（GTase）或转肽酶（TPase）活性的希瓦氏菌属 oneidensis PBP1a 变体无法维持正常的形态和细胞包膜完整性。同样，SoPBP1b 变体也无法补偿 SoPBP1a 的缺失。此外，SoPBP1a 变体的过度表达，但不是 SoPBP1b 变体的过度表达，对希瓦氏菌属 oneidensis 野生型细胞的细胞形态有不利影响。总的来说，我们的结果表明，SoPBP1a 的组合酶活性对于细胞壁的动态平衡是必不可少的。
