Pilsl H, Smajs D, Braun V
Mikrobiologie/Membranphysiologie, Universität Tübingen, Tübingen, Germany.
J Bacteriol. 1998 Aug;180(16):4111-5. doi: 10.1128/JB.180.16.4111-4115.1998.
The hydrophobic C terminus of pore-forming colicins associates with and inserts into the cytoplasmic membrane and is the target of the respective immunity protein. The hydrophobic region of colicin U of Shigella boydii was mutated to identify determinants responsible for recognition of colicin U by the colicin U immunity protein. Deletion of the tip of the hydrophobic hairpin of colicin U resulted in a fully active colicin that was no longer inactivated by the colicin U immunity protein. Replacement of eight amino acids at the tip of the colicin U hairpin by the corresponding amino acids of the related colicin B resulted in colicin U(575-582ColB), which was inactivated by the colicin U immunity protein to 10% of the level of inactivation of the wild-type colicin U. The colicin B immunity protein inactivated colicin U(575-582ColB) to the same degree. These results indicate that the tip of the hydrophobic hairpin of colicin U and of colicin B mainly determines the interaction with the corresponding immunity proteins and is not required for colicin activity. Comparison of these results with published data suggests that interhelical loops and not membrane helices of pore-forming colicins mainly interact with the cognate immunity proteins and that the loops are located in different regions of the A-type and E1-type colicins. The colicin U immunity protein forms four transmembrane segments in the cytoplasmic membrane, and the N and C termini face the cytoplasm.
形成孔道的大肠杆菌素的疏水C末端与细胞质膜结合并插入其中，是相应免疫蛋白的作用靶点。对痢疾志贺氏菌的大肠杆菌素U的疏水区域进行突变，以确定负责被大肠杆菌素U免疫蛋白识别的决定因素。删除大肠杆菌素U疏水发夹的末端会产生一种完全有活性的大肠杆菌素，它不再被大肠杆菌素U免疫蛋白灭活。用相关的大肠杆菌素B的相应氨基酸替换大肠杆菌素U发夹末端的八个氨基酸，得到大肠杆菌素U(575 - 582ColB)，它被大肠杆菌素U免疫蛋白灭活至野生型大肠杆菌素U灭活水平的10%。大肠杆菌素B免疫蛋白对大肠杆菌素U(575 - 582ColB)的灭活程度相同。这些结果表明，大肠杆菌素U和大肠杆菌素B疏水发夹的末端主要决定了与相应免疫蛋白的相互作用，且对大肠杆菌素活性不是必需的。将这些结果与已发表的数据进行比较表明，形成孔道的大肠杆菌素的螺旋间环而非膜螺旋主要与同源免疫蛋白相互作用，并且这些环位于A 型和E1型大肠杆菌素的不同区域。大肠杆菌素U免疫蛋白在细胞质膜中形成四个跨膜片段，其N末端和C末端面向细胞质。
