Schramm E, Olschläger T, Tröger W, Braun V
Mikrobiologie II, Universität Tübingen, Federal Republic of Germany.
Mol Gen Genet. 1988 Jan;211(1):176-82. doi: 10.1007/BF00338410.
Cells of Escherichia coli containing the cbi locus on plasmids are immune to colicin B which kills cells by dissipating the membrane potential through pore formation in the cytoplasmic membrane. The nucleotide sequence of the cbi region was determined. It contains an open reading frame for a polypeptide consisting of 175 amino acids. The amino acid sequence is homologous to the primary structure of the colicin A immunity protein. This, and the strong homology between the pore-forming domains of colicins A and B suggests a common evolutionary origin for both colicins. The immunity protein could be identified following strong overexpression of cbi. The electrophoretically determined molecular weight of 20,000 was close to the calculated molecular weight of 20,185. The protein contains four large hydrophobic regions. The immunity protein was localized in the membrane fraction and was mainly contained in the cytoplasmic membrane. It is proposed that the immunity protein inactivates the colicin in the cytoplasmic membrane.
含有位于质粒上cbi位点的大肠杆菌细胞对大肠菌素B具有免疫性，大肠菌素B通过在细胞质膜上形成孔道来耗散膜电位从而杀死细胞。测定了cbi区域的核苷酸序列。它包含一个由175个氨基酸组成的多肽的开放阅读框。该氨基酸序列与大肠菌素A免疫蛋白的一级结构同源。这一点，以及大肠菌素A和B的成孔结构域之间的高度同源性表明这两种大肠菌素有着共同的进化起源。在cbi强烈过表达后可以鉴定出免疫蛋白。电泳测定的分子量为20,000，与计算出的分子量20,185接近。该蛋白包含四个大的疏水区。免疫蛋白定位于膜组分中，主要存在于细胞质膜中。有人提出免疫蛋白在细胞质膜中使大肠菌素失活。
