Two class A high-molecular-weight penicillin-binding proteins of Bacillus subtilis play redundant roles in sporulation
Two class A high-molecular-weight penicillin-binding proteins of Bacillus subtilis play redundant roles in sporulation
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DOI：
10.1128/jb.183.20.6046-6053.2001
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发表时间：
2001-10-01
影响因子：
3.2
通讯作者：
Popham, DL
中科院分区：
文献类型：
--
作者：
McPherson, DC;Driks, A;Popham, DL
枯草芽孢杆菌的四个A类青霉素结合蛋白(PBPs)似乎在聚合营养细胞和孢子壁的肽聚糖(PG)链方面发挥了功能上的冗余作用。由于yWhE基因产物与青霉素结合，故将该基因和基因产物分别重命名为pbpG和pBP2d。缺乏多个A类PBPs的突变株的构建表明，虽然PBP2d在营养体壁的合成中没有明显的作用，但它确实在孢子PG的合成中发挥了作用。PbpG缺失突变体产生的孢子PG在结构上与野生型相似；然而，电子显微镜显示，在相当数量的这些孢子中，PG没有完全包围孢子芯。在pbpF pbpG双突变体中，每个产生的孢子都存在这种孢子PG缺陷，这表明这两个基因产物起着部分冗余的作用。双突变体产生了正常数量的孢子PG，但经常在前孢子两侧大量产生。双突变孢子PG的结构变化表明，皮层PG合成不当，包括胞壁β-内酰胺和L-丙氨酸侧链的生成减少了一倍，交联度略有增加。PbpF pbpG双突变体产孢子基因表达正常，但双突变体孢子未能进入休眠状态，孢子PG降解。我们认为，这两个前孔合成的PBPs是合成孢子生殖细胞壁所必需的，第一层孢子PG是在内前孔膜表面合成的，而在没有生殖细胞壁的情况下，细胞缺乏通过外前孔膜上的蛋白质正确合成孢子皮质(孢子PG的外层)所需的模板。
The four class A penicillin-binding proteins (PBPs) of Bacillus subtilis appear to play functionally redundant roles in polymerizing the peptidoglycan (PG) strands of the vegetative-cell and spore walls. The ywhE product was shown to bind penicillin, so the gene and gene product were renamed pbpG and PBP2d, respectively. Construction of mutant strains lacking multiple class A PBPs revealed that, while PBP2d plays no obvious role in vegetative-wall synthesis, it does play a role in spore PG synthesis. A pbpG null mutant produced spore PG structurally similar to that of the wild type; however, electron microscopy revealed that in a significant number of these spores the PG did not completely surround the spore core. In a pbpF pbpG double mutant this spore PG defect was apparent in every spore produced, indicating that these two gene products play partially redundant roles. A normal amount of spore PG was produced in the double mutant, but it was frequently produced in large masses on either side of the forespore. The double-mutant spore PG had structural alterations indicative of improper cortex PG synthesis, including twofold decreases in production of muramic delta -lactam and L-alanine side chains and a slight increase in cross-linking. Sporulation gene expression in the pbpF pbpG double mutant was normal, but the double-mutant spores failed to reach dormancy and subsequently degraded their spore PG. We suggest that these two forespore-synthesized PBPs are required for synthesis of the spore germ cell wall, the first layer of spore PG synthesized on the surface of the inner forespore membrane, and that in the absence of the germ cell wall the cells lack a template needed for proper synthesis of the spore cortex, the outer layers of spore PG, by proteins on the outer forespore membrane.