Koch A L
Biology Department, Indiana University, Bloomington 47405.
Res Microbiol. 1990 Jun;141(5):529-41. doi: 10.1016/0923-2508(90)90017-k.
Because the wall of Gram-negative bacteria is thin, the mechanism for safe enlargement of the cell is subject to strong constraints. Several models for wall growth have been proposed; in the order that they have been proposed, these include: 1) an "allosteric" model in which the critical autolysin is only functional if the bond to be cleaved is near a covalently cross-linked, but unstretched oligopeptide; 2) a model in which the cell wall is thick enough to enlarge by the "inside-to-outside" mode characteristic of Gram-positive rods; 3) a "patches" model, recently proposed by Höltje, in which only parts of the cell wall are thickened at any one time; 4) a new multienzyme model in which the transpeptidase/autolysin complex cleaves one cross-linked oligopeptidoglycan chain for every two nascent chains covalently polymerized to the sacculus. These models are considered and contrasted. While none can be rigourously excluded, no. 4 is favoured. All models as applied to the Gram-negative rod-shaped bacteria require special, extraordinary features for their autolysins. These features have not been found with any other class of enzymes, but are essential to permit safe cell expansion.
由于革兰氏阴性菌的细胞壁较薄，细胞安全增大的机制受到严格限制。已经提出了几种细胞壁生长模型；按照提出的顺序，这些模型包括：1）“变构”模型，其中关键自溶素只有在待切割的键靠近共价交联但未拉伸的寡肽时才起作用；2）一种模型，其中细胞壁足够厚，可以通过革兰氏阳性杆菌特有的“由内向外”模式增大；3）“斑块”模型，由霍尔特耶最近提出，其中在任何时候只有部分细胞壁会增厚；4）一种新的多酶模型，其中转肽酶/自溶素复合物每共价聚合两条新生链到细胞壁时就切割一条交联的寡肽聚糖链。对这些模型进行了考虑和对比。虽然没有一个模型可以被严格排除，但第4个模型更受青睐。所有应用于革兰氏阴性杆状细菌的模型都要求其自溶素具有特殊的、非凡的特征。这些特征在任何其他类别的酶中都未发现，但对于允许细胞安全扩张至关重要。
