Bacterial Cell Biology and Physiology, Swammerdam Institute for Life Science, University of Amsterdam, 1098 XH Amsterdam, The Netherlands.
Department of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands.
Int J Mol Sci. 2021 Nov 9;22(22):12101. doi: 10.3390/ijms222212101.
The BAM is a macromolecular machine responsible for the folding and the insertion of integral proteins into the outer membrane of diderm Gram-negative bacteria. In , it consists of a transmembrane β-barrel subunit, BamA, and four outer membrane lipoproteins (BamB-E). Using BAM-specific antibodies, in cells, the complex is shown to localize in the lateral wall in foci. The machinery was shown to be enriched at midcell with specific cell cycle timing. The inhibition of septation by aztreonam did not alter the BAM midcell localization substantially. Furthermore, the absence of late cell division proteins at midcell did not impact BAM timing or localization. These results imply that the BAM enrichment at the site of constriction does not require an active cell division machinery. Expression of the Tre1 toxin, which impairs the FtsZ filamentation and therefore midcell localization, resulted in the complete loss of BAM midcell enrichment. A similar effect was observed for YidC, which is involved in the membrane insertion of cell division proteins in the inner membrane. The presence of the Z-ring is needed for preseptal peptidoglycan (PG) synthesis. As BAM was shown to be embedded in the PG layer, it is possible that BAM is inserted preferentially simultaneously with de novo PG synthesis to facilitate the insertion of OMPs in the newly synthesized outer membrane.
BAM 是一种负责将整合蛋白折叠并插入二肽革兰氏阴性细菌外膜的大分子机器。在 中，它由一个跨膜β桶亚基 BamA 和四个外膜脂蛋白（BamB-E）组成。使用 BAM 特异性抗体，在 细胞中，该复合物被显示定位在侧墙的焦点中。该机器在中细胞处被富集，具有特定的细胞周期时间。阿托龙姆抑制分隔不会显著改变 BAM 的中细胞定位。此外，中细胞处缺乏晚期细胞分裂蛋白不会影响 BAM 的时间或定位。这些结果表明，在收缩部位的 BAM 富集不需要活跃的细胞分裂机制。表达 Tre1 毒素会损害 FtsZ 丝状体化，从而导致 BAM 中细胞富集的完全丧失。类似的效应也观察到 YidC，它参与了内膜中细胞分裂蛋白的膜插入。Z 环的存在是间隔前肽聚糖（PG）合成所必需的。由于 BAM 被嵌入 PG 层中，因此 BAM 可能与新合成的外膜中的 OMPs 一起优先插入，以促进其插入。
