Davies Robert L, Lee Inkyoung
Division of Infection and Immunity, Institute of Biomedical and Life Sciences, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
J Bacteriol. 2004 Sep;186(17):5741-52. doi: 10.1128/JB.186.17.5741-5752.2004.
The OmpA (or heat-modifiable) protein is a major structural component of the outer membranes of gram-negative bacteria. The protein contains eight membrane-traversing beta-strands and four surface-exposed loops. The genetic diversity and molecular evolution of OmpA were investigated in 31 Mannheimia (Pasteurella) haemolytica, 6 Mannheimia glucosida, and 4 Pasteurella trehalosi strains by comparative nucleotide sequence analysis. The OmpA proteins of M. haemolytica and M. glucosida contain four hypervariable domains located at the distal ends of the surface-exposed loops. The hypervariable domains of OmpA proteins from bovine and ovine M. haemolytica isolates are very different but are highly conserved among strains from each of these two host species. Fourteen different alleles representing four distinct phylogenetic classes, classes I to IV, were identified in M. haemolytica and M. glucosida. Class I, II, and IV alleles were associated with bovine M. haemolytica, ovine M. haemolytica, and M. glucosida strains, respectively, whereas class III alleles were present in certain M. haemolytica and M. glucosida isolates. Class I and II alleles were associated with divergent lineages of bovine and ovine M. haemolytica strains, respectively, indicating a history of horizontal DNA transfer and assortative (entire gene) recombination. Class III alleles have mosaic structures and were derived by horizontal DNA transfer and intragenic recombination. Our findings suggest that OmpA is under strong selective pressure from the host species and that it plays an important role in host adaptation. It is proposed that the OmpA protein of M. haemolytica acts as a ligand and is involved in binding to specific host cell receptor molecules in cattle and sheep. P. trehalosi expresses two OmpA homologs that are encoded by different tandemly arranged ompA genes. The P. trehalosi ompA genes are highly diverged from those of M. haemolytica and M. glucosida, and evidence is presented to suggest that at least one of these genes was acquired by horizontal DNA transfer.
外膜蛋白A（或热修饰蛋白）是革兰氏阴性菌外膜的主要结构成分。该蛋白含有8个跨膜β链和4个表面暴露环。通过比较核苷酸序列分析，对31株溶血曼氏杆菌（巴斯德氏菌属）、6株葡萄糖苷曼氏杆菌和4株海藻糖巴斯德氏菌中的外膜蛋白A的遗传多样性和分子进化进行了研究。溶血曼氏杆菌和葡萄糖苷曼氏杆菌的外膜蛋白A含有位于表面暴露环远端的4个高变区。来自牛和羊的溶血曼氏杆菌分离株的外膜蛋白A高变区差异很大，但在这两个宿主物种的各菌株中高度保守。在溶血曼氏杆菌和葡萄糖苷曼氏杆菌中鉴定出代表4个不同系统发育类别的14个不同等位基因，即I至IV类。I类、II类和IV类等位基因分别与牛溶血曼氏杆菌、羊溶血曼氏杆菌和葡萄糖苷曼氏杆菌菌株相关，而III类等位基因存在于某些溶血曼氏杆菌和葡萄糖苷曼氏杆菌分离株中。I类和II类等位基因分别与牛和羊溶血曼氏杆菌菌株的不同谱系相关，表明存在水平DNA转移和分类（全基因）重组的历史。III类等位基因具有镶嵌结构，是通过水平DNA转移和基因内重组产生的。我们的研究结果表明，外膜蛋白A受到宿主物种的强烈选择压力，并且在宿主适应中起重要作用。有人提出，溶血曼氏杆菌的外膜蛋白A作为配体，参与与牛和羊中特定宿主细胞受体分子的结合。海藻糖巴斯德氏菌表达两种由不同串联排列的ompA基因编码的外膜蛋白A同源物。海藻糖巴斯德氏菌的ompA基因与溶血曼氏杆菌和葡萄糖苷曼氏杆菌的ompA基因高度不同，并且有证据表明这些基因中至少有一个是通过水平DNA转移获得的。
