Laboratory of Bacterial Genetics, Gdansk University of Technology, 80-233 Gdansk, Poland.
Int J Mol Sci. 2022 Aug 26;23(17):9706. doi: 10.3390/ijms23179706.
Lipopolysaccharide (LPS) constitutes the major component of the outer membrane and is essential for bacteria, such as . Recent work has revealed the essential roles of LapB and LapC proteins in regulating LPS amounts; although, if any additional partners are involved is unknown. Examination of proteins co-purifying with LapB identified LapD as a new partner. The purification of LapD reveals that it forms a complex with several proteins involved in LPS and phospholipid biosynthesis, including FtsH-LapA/B and Fab enzymes. Loss of LapD causes a reduction in LpxC amounts and vancomycin sensitivity, which can be restored by mutations that stabilize LpxC (mutations in , and genes), revealing that LapD acts upstream of LapB-FtsH in regulating LpxC amounts. Interestingly, LapD absence results in the substantial retention of LPS in the inner membranes and synthetic lethality when either the lauroyl or the myristoyl acyl transferase is absent, which can be overcome by single-amino acid suppressor mutations in LPS flippase MsbA, suggesting LPS translocation defects in Δ bacteria. Several genes whose products are involved in cell envelope homeostasis, including , , and , become essential in LapD's absence. Furthermore, the overproduction of acyl carrier protein AcpP or transcriptional factors DksA, SrrA can overcome certain defects of the LapD-lacking strain.
脂多糖（LPS）构成了外膜的主要成分，对于细菌等生物体至关重要。最近的研究揭示了 LapB 和 LapC 蛋白在调节 LPS 含量方面的重要作用；然而，是否有其他的伴侣蛋白参与其中还不清楚。对与 LapB 共纯化的蛋白质进行分析，发现 LapD 是一个新的伴侣蛋白。LapD 的纯化表明它与参与 LPS 和磷脂生物合成的几种蛋白质形成复合物，包括 FtsH-LapA/B 和 Fab 酶。LapD 的缺失会导致 LpxC 含量减少和万古霉素敏感性增加，而通过稳定 LpxC 的突变（突变在 、 和 基因）可以恢复这种情况，这表明 LapD 在调节 LpxC 含量方面在上游作用于 LapB-FtsH。有趣的是，当缺少棕榈酰或肉豆蔻酰转移酶时，LapD 的缺失会导致 LPS 在内膜中的大量滞留和合成致死，而 LPS 翻转酶 MsbA 的单个氨基酸抑制突变可以克服这种情况，这表明Δ菌中存在 LPS 转位缺陷。几个与细胞包膜稳态相关的基因，包括 、 、 和 ，在 LapD 缺失时变得必需。此外，酰基载体蛋白 AcpP 或转录因子 DksA、SrrA 的过度表达可以克服 LapD 缺失菌株的某些缺陷。
