Pinne Marija, Denker Katrin, Nilsson Elin, Benz Roland, Bergström Sven
Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden.
J Bacteriol. 2006 Jun;188(12):4207-17. doi: 10.1128/JB.00302-06.
The Borrelia burgdorferi genome exhibits redundancy, with many plasmid-carried genes belonging to paralogous gene families. It has been suggested that certain paralogs may be necessary in various environments and that they are differentially expressed in response to different conditions. The chromosomally located p13 gene which codes for a channel-forming protein belongs to paralog family 48, which consists of eight additional genes. Of the paralogous genes from family 48, the BBA01 gene has the highest homology to p13. Herein, we have inactivated the BBA01 gene in B. burgdorferi strain B31-A. This mutant shows no apparent phenotypic difference compared to the wild type. However, analysis of BBA01 in a C-terminal protease A (CtpA)-deficient background revealed that like P13, BBA01 is posttranslationally processed at its C terminus. Elevated BBA01 expression was obtained in strains with the BBA01 gene introduced on the shuttle vector compared to the wild-type strain. We could further demonstrate that BBA01 is a channel-forming protein with properties surprisingly similar to those of P13. The single-channel conductance, of about 3.5 nS, formed by BBA01 is comparable to that of P13, which together with the high degree of sequence similarity suggests that the two proteins may have similar and interchangeable functions. This is further strengthened by the up-regulation of the BBA01 protein and its possible localization in the outer membrane in a p13 knockout strain, thus suggesting that P13 can be replaced by BBA01.
伯氏疏螺旋体基因组存在冗余现象，许多携带质粒的基因属于旁系同源基因家族。有人提出，某些旁系同源基因在不同环境中可能是必需的，并且它们会根据不同条件进行差异表达。位于染色体上的编码通道形成蛋白的p13基因属于旁系同源家族48，该家族还包括另外八个基因。在家族48的旁系同源基因中，BBA01基因与p13的同源性最高。在此，我们使伯氏疏螺旋体B31 - A菌株中的BBA01基因失活。与野生型相比，该突变体没有明显的表型差异。然而，在缺乏C末端蛋白酶A（CtpA）的背景下对BBA01进行分析发现，与P13一样，BBA01在其C末端进行翻译后加工。与野生型菌株相比，在携带穿梭载体导入BBA01基因的菌株中获得了更高的BBA01表达。我们进一步证明BBA01是一种通道形成蛋白，其特性与P13惊人地相似。BBA01形成的单通道电导约为3.5 nS，与P13相当，这与高度的序列相似性一起表明这两种蛋白质可能具有相似且可互换的功能。p13基因敲除菌株中BBA01蛋白的上调及其可能在外膜中的定位进一步强化了这一点，从而表明P13可以被BBA01取代。
