Institute of Molecular Medicine, College of Medicine, National Cheng-Kung University, Tainan City 704-56, Taiwan, ROC.
Center of Infectious Disease and Signal Transduction, College of Medicine, National Cheng-Kung University, Tainan City 704-56, Taiwan, ROC.
Microbiology (Reading). 2018 Mar;164(3):299-307. doi: 10.1099/mic.0.000614. Epub 2018 Jan 25.
Bacterial cells are covered with peptidoglycan (PG) layer(s), serving as the cellular exoskeleton. The PG sacculus changes its shape during cell growth, and thus both the synthesis and disassembly of PG are important for cell proliferation. In Bacillus subtilis, four dl-endopeptidases (DLEPases; LytE, LytF, CwlO and CwlS) are involved in the maintenance of cell morphology. The lytE cwlO double mutant exhibits synthetic lethality and defective cell elongation, while the lytE lytF cwlS triple mutant exhibits defective cell separation, albeit with septum formation. LytE is involved in both cell separation and elongation. We propose that DLEPases have varied roles in cell separation and elongation. To determine these roles, the catalytic domain of LytE was substituted with another catalytic domain that digests the other bonds in PG. By using the chimeric enzymes, we assessed the suppression of the synthetic lethality by the cell elongation defect and the disruption of chain morphology by the cell separation defect. All the constructed chimeric enzymes suppressed the cell separation defect, restoring the chain morphology. Digestion at any position of PG broke the linkage between two daughter cells, releasing them from each other. However, only d,d-endopeptidases suppressed the lack of DLEPase in the lytE cwlO double mutant. This indicated that the release of tension on the expanding PG sacculus is not the sole essential function of DLEPases. Considering that the structure of the digested PG is important for cell elongation, the digested product might be reused in the growth process in some way.
细菌细胞被肽聚糖 (PG) 层覆盖，作为细胞的外骨骼。PG 囊在细胞生长过程中改变形状，因此 PG 的合成和分解对于细胞增殖都很重要。在枯草芽孢杆菌中，有四个 dl-内肽酶（DLEPases；LytE、LytF、CwlO 和 CwlS）参与维持细胞形态。lytE cwlO 双突变体表现出合成致死性和细胞伸长缺陷，而 lytE lytF cwlS 三突变体表现出细胞分离缺陷，尽管有隔膜形成。LytE 参与细胞分离和伸长。我们提出 DLEPases 在细胞分离和伸长中具有不同的作用。为了确定这些作用，用另一种消化 PG 中其他键的催化结构域替换了 LytE 的催化结构域。通过使用嵌合酶，我们评估了细胞伸长缺陷对合成致死性的抑制作用以及细胞分离缺陷对链形态的破坏作用。所有构建的嵌合酶都抑制了细胞分离缺陷，恢复了链形态。PG 中任何位置的消化都会破坏两个子细胞之间的连接，使它们彼此分离。然而，只有 d,d-内肽酶抑制了 lytE cwlO 双突变体中缺乏 DLEPase 的作用。这表明 DLEPases 释放扩张的 PG 囊上的张力不是其唯一的必要功能。考虑到消化的 PG 结构对于细胞伸长很重要，消化产物可能以某种方式在生长过程中被重新利用。
