Biochimie et Génétique Moléculaire Bactérienne, Institut des Sciences de la Vie, Université Catholique de Louvain, Louvain-la-Neuve 1348, Belgium.
J Biol Chem. 2010 Jul 30;285(31):24003-13. doi: 10.1074/jbc.M110.143636. Epub 2010 Jun 4.
Cell wall peptidoglycan assembly is a tightly regulated process requiring the combined action of multienzyme complexes. In this study we provide direct evidence showing that substrate transformations occurring at the different stages of this process play a crucial role in the spatial and temporal coordination of the cell wall synthesis machinery. Peptidoglycan substrate alteration was investigated in the Gram-positive bacterium Lactococcus lactis by substituting the peptidoglycan precursor biosynthesis genes of this bacterium for those of the vancomycin-resistant bacterium Lactobacillus plantarum. A set of L. lactis mutant strains in which the normal d-Ala-ended precursors were partially or totally replaced by d-Lac-ended precursors was generated. Incorporation of the altered precursor into the cell wall induced morphological changes arising from a defect in cell elongation and cell separation. Structural analysis of the muropeptides confirmed that the activity of multiple enzymes involved in peptidoglycan synthesis was altered. Optimization of this altered pathway was necessary to increase the level of vancomycin resistance conferred by the utilization of d-Lac-ended peptidoglycan precursors in the mutant strains. The implications of these findings on the control of bacterial cell morphogenesis and the mechanisms of vancomycin resistance are discussed.
细胞壁肽聚糖装配是一个受到严格调控的过程，需要多酶复合物的协同作用。在本研究中，我们提供了直接证据表明，该过程不同阶段发生的底物转化在细胞壁合成机制的时空协调中起着至关重要的作用。通过将革兰氏阳性菌乳球菌的肽聚糖前体生物合成基因替换为耐万古霉素的植物乳杆菌的基因，研究了肽聚糖底物的改变。生成了一组 L. lactis 突变株，其中正常的 d-Ala 末端前体被部分或完全替换为 d-Lac 末端前体。改变的前体掺入细胞壁引起了源于细胞伸长和细胞分离缺陷的形态变化。寡肽的结构分析证实，参与肽聚糖合成的多种酶的活性发生了改变。优化该改变的途径对于增加突变株中利用 d-Lac 末端肽聚糖前体赋予的万古霉素抗性水平是必要的。讨论了这些发现对细菌细胞形态发生的控制和万古霉素抗性机制的影响。
