Kim Yung Jae, Choi Byoung Jun, Park Si Hyoung, Lee Han Byeol, Son Ji Eun, Choi Umji, Chi Won-Jae, Lee Chang-Ro
Department of Biological Sciences, Myongji University, Yongin, South Korea.
Biological and Genetic Resource Assessment Division, National Institute of Biological Resource, Incheon, South Korea.
Front Microbiol. 2021 Jun 30;12:677739. doi: 10.3389/fmicb.2021.677739. eCollection 2021.
Peptidoglycan (PG) hydrolases play important roles in various aspects of bacterial physiology, including cytokinesis, PG synthesis, quality control of PG, PG recycling, and antibiotic resistance. However, the regulatory mechanisms of their expression are poorly understood. In this study, we have uncovered novel regulatory mechanisms of the protein levels of the synthetically lethal PG endopeptidases MepS and MepM, which are involved in PG synthesis. A mutant defective for both MepS and MepM was lethal in an amino acid-rich medium, whereas it exhibited almost normal growth in a minimal medium, suggesting the expendability of MepS and MepM in a minimal medium. Protein levels of MepS and MepM dramatically decreased in the minimal medium. Although MepM was revealed as a substrate of Prc, a periplasmic protease involved in the proteolysis of MepS, only the decrease in the MepS level in the minimal medium was affected by the depletion. Phenotypic and biochemical analyses showed that the presence of aromatic amino acids in the medium induced the accumulation of MepS, but not MepM, while the presence of glutamate increased the level of MepM, but not MepS. Together, these results demonstrate that the protein levels of the two major PG endopeptidases are regulated in an amino acid availability-dependent manner, but their molecular mechanisms and signaling are significantly distinct.
肽聚糖（PG）水解酶在细菌生理学的各个方面发挥着重要作用，包括胞质分裂、PG合成、PG质量控制、PG循环利用和抗生素抗性。然而，其表达的调控机制仍知之甚少。在本研究中，我们发现了参与PG合成的合成致死性PG内肽酶MepS和MepM蛋白水平的新调控机制。MepS和MepM双缺陷突变体在富含氨基酸的培养基中是致死的，而在基本培养基中其生长几乎正常，这表明在基本培养基中MepS和MepM是可消耗的。在基本培养基中，MepS和MepM的蛋白水平显著降低。虽然MepM被发现是Prc的底物，Prc是一种参与MepS蛋白水解的周质蛋白酶，但在基本培养基中只有MepS水平的降低受到该蛋白酶缺失的影响。表型和生化分析表明，培养基中芳香族氨基酸的存在诱导了MepS的积累，但未诱导MepM的积累，而谷氨酸的存在增加了MepM的水平，但未增加MepS的水平。总之，这些结果表明，两种主要的PG内肽酶的蛋白水平以氨基酸可用性依赖的方式受到调控，但其分子机制和信号传导明显不同。
