Taschner P E, Ypenburg N, Spratt B G, Woldringh C L
Department of Molecular Cell Biology, University of Amsterdam, The Netherlands.
J Bacteriol. 1988 Oct;170(10):4828-37. doi: 10.1128/jb.170.10.4828-4837.1988.
The pbpB gene product penicillin-binding protein 3 (PBP3) of Escherichia coli is one of the major targets of beta-lactam antibiotics. At the permissive temperature, the temperature-sensitive pbpBr1 mutant, which was obtained after selection for increased resistance to cephalexin, shows a dramatic change in shape which has never been observed before; the polar caps are pointed. We show that the substitution of amino acid Asn-361 by Ser, previously shown to be responsible for increased cephalexin resistance and for temperature sensitivity, causes the pointed polar caps. However, comparison of the morphological and physiological characteristics of the pbpBr1 mutant with those of other pbpB mutants suggests that the formation of pointed polar caps is not correlated with temperature sensitivity or cephalexin resistance. Partial inactivation of PBP3 by subinhibitory concentrations of cephalexin, furazlocillin, and piperacillin resulted in the formation of slightly pointed polar caps, suggesting that the shape of the polar caps is correlated with PBP3 activity. The large change in the shape of the polar caps was accompanied by a small change in the kinetics of peptidoglycan synthesis and in the local rate of surface synthesis activity along the cell envelope.
大肠杆菌的pbpB基因产物青霉素结合蛋白3（PBP3）是β-内酰胺类抗生素的主要靶点之一。在允许温度下，对头孢氨苄抗性增强的温度敏感型pbpBr1突变体在选择后表现出前所未有的显著形状变化；极帽变尖。我们发现，先前已证明导致头孢氨苄抗性增强和温度敏感性的将氨基酸Asn-361替换为Ser会导致极帽变尖。然而，将pbpBr1突变体与其他pbpB突变体的形态和生理特征进行比较表明，极帽变尖的形成与温度敏感性或头孢氨苄抗性无关。亚抑制浓度的头孢氨苄、呋唑西林和哌拉西林对PBP3的部分失活导致极帽略微变尖，这表明极帽的形状与PBP3活性相关。极帽形状的巨大变化伴随着肽聚糖合成动力学以及沿细胞膜表面合成活性局部速率的微小变化。
