Howard S P, Lindsay L
University of Regina, Saskatchewan, Canada.
J Bacteriol. 1998 Jun;180(12):3026-30. doi: 10.1128/JB.180.12.3026-3030.1998.
The lipid modification and processing of a number of colicin lysis proteins take place exceedingly slowly and result in the release of a stable signal peptide. It is possible that this peptide or the presence of lipid-modified precursors which result from the slow processing plays a role in the release of colicins and in the quasilysis that occurs in induced colicinogenic cultures. We used in vitro mutagenesis and pulse-chase radiolabeling and immunoprecipitation to examine the reasons for the slow processing and signal peptide degradation reactions for the colicin A lysis protein (Cal). In one mutant, isoleucine 13 was replaced with serine, and in another, alanine 18, the last residue of the signal peptide, was replaced with glycine. In each case, the mutation caused a striking increase in the rate of maturation of the precursor, and in the case of the serine 13 derivative, the mutation also destabilized the signal peptide. A precursor containing both of these mutations was completely matured and its signal sequence degraded within seconds of its synthesis. The release of colicin A and the quasilysis of producing cultures were unchanged for each of these mutants, indicating that neither the stable signal peptide nor lipid-modified processing intermediates of Cal are required for either of these events in wild-type cells.
多种大肠杆菌素裂解蛋白的脂质修饰和加工过程极其缓慢，并导致稳定信号肽的释放。有可能是这种肽或缓慢加工产生的脂质修饰前体的存在，在大肠杆菌素的释放以及诱导产大肠杆菌素培养物中发生的准裂解过程中发挥了作用。我们使用体外诱变、脉冲追踪放射性标记和免疫沉淀来研究大肠杆菌素A裂解蛋白（Cal）加工缓慢和信号肽降解反应的原因。在一个突变体中，异亮氨酸13被丝氨酸取代，在另一个突变体中，信号肽的最后一个残基丙氨酸18被甘氨酸取代。在每种情况下，突变都导致前体成熟速率显著增加，并且在丝氨酸13衍生物的情况下，突变还使信号肽不稳定。含有这两种突变的前体在合成后几秒钟内就完全成熟，其信号序列也被降解。这些突变体中每种突变体的大肠杆菌素A释放和产菌培养物的准裂解均未改变，这表明在野生型细胞中，无论是稳定的信号肽还是Cal的脂质修饰加工中间体，对于这些事件中的任何一个都不是必需的。
