Koch A L
Biology Department, Indiana University, Bloomington 47405, USA.
FEMS Microbiol Lett. 1998 May 1;162(1):127-34. doi: 10.1111/j.1574-6968.1998.tb12989.x.
The murein wall in Gram-negative bacteria is so thin that the mechanism of growth is necessarily complicated. From analytical data of murein components, Höltje suggested a model for the growth mechanism that would lead to safe wall enlargement. The model depended on the formation of trimers of peptidoglycan disaccharides linked via their pentapeptides. In the 'three-for-one' model three oligopeptidoglycan chains are linked to each other in the usual linkages between the carboxyl group of D-alanine residues and the epsilon-amino group of diaminopimelic acid residues; these are designated 'tail-to-tail' linkages. This three-chained raft is then linked to the stress-bearing wall via the formation of trimers, defined as three peptide chains linked together by tail-to-tail linkages. Then by autolyzing the oldest bonds in each trimer, the old chain is excised and the raft becomes part of the stress-bearing wall and the wall is enlarged. There is a problem with the three-for-one model in that it demands a precise fitting of the prefabricated raft of three crosslinked chains to a stress-bearing chain in the wall fabric to allow the series of trimer linkages to form. Because the wall, when bearing stress, must be pulled into a 'honeycomb' structure, the end-to-end distance would be shortened. The possibility is raised here that the glycan chains in the stress-bearing wall are stretched to a sufficient degree by the cell's turgor pressure to compensate for its zig-zag structure; this could allow the model to function. A calculation is presented that assumes that the area of the pores in the fabric, called tessera, is maximized by the cell's turgor pressure. In this case the glycan chain must stretch 10% (and the end-to-end distance of peptide strands stretch 28%) so that the end-to-end distance of a glycan chain in the stress-bearing wall and the unstretched nascent wall can be the same and permit indefinite stable growth.
革兰氏阴性菌的胞壁质壁非常薄，以至于其生长机制必然很复杂。根据胞壁质成分的分析数据，霍尔特耶提出了一个生长机制模型，该模型将导致细胞壁安全扩大。该模型依赖于通过其五肽连接的肽聚糖二糖三聚体的形成。在“三对一”模型中，三条寡肽聚糖链通过D - 丙氨酸残基的羧基与二氨基庚二酸残基的ε - 氨基之间的通常连接相互连接；这些被称为“尾对尾”连接。然后，这个三链筏通过三聚体的形成与承受压力的细胞壁相连，三聚体定义为通过尾对尾连接连接在一起的三条肽链。然后，通过自溶每个三聚体中最旧的键，切除旧链，筏成为承受压力的细胞壁的一部分，细胞壁得以扩大。“三对一”模型存在一个问题，即它要求预先制造的由三条交联链组成的筏精确地与细胞壁结构中的承受压力的链相匹配，以允许形成一系列三聚体连接。因为细胞壁在承受压力时必须被拉成“蜂窝”结构，端到端的距离会缩短。这里提出一种可能性，即承受压力的细胞壁中的聚糖链通过细胞的膨压被拉伸到足够的程度，以补偿其锯齿状结构；这可以使模型发挥作用。本文给出了一个计算，假设细胞壁结构中称为镶嵌体的孔隙面积通过细胞的膨压最大化。在这种情况下，聚糖链必须拉伸10%（肽链的端到端距离拉伸28%），这样承受压力的细胞壁中聚糖链的端到端距离与未拉伸的新生细胞壁的端到端距离可以相同，并允许无限期稳定生长。
