Simmons W L, Zuhua C, Glass J I, Simecka J W, Cassell G H, Watson H L
Department of Microbiology, University of Alabama at Birmington School of Medicine 35294, USA.
Infect Immun. 1996 Feb;64(2):472-9. doi: 10.1128/iai.64.2.472-479.1996.
Although the variation of V-1 antigens of Mycoplasma pulmonis has been correlated with variable expression of the cytadherence properties of this organism and has been implicated as a virulence determining factor in M. pulmonis-induced murine respiratory disease, the precise function of these antigens remains unknown. We have cloned and characterized genes encoding V-1 from two M. pulmonis UAB CT V-1 variants that differ in hemadsorption properties. A comparison of the nucleotide sequences revealed that these two variant genes were identical in the 5'-most 724 nucleotides. Regions of extensive divergence that contained repeated sequences were found 3' to this conserved region. On the basis of their deduced amino acid sequences, one variant expressed a V-1 protein of 94.2 kDa presumptively containing 40 repeats of 17 amino acids and the other expressed a protein of 27.4 kDa consisting 2 direct, noncontiguous 9-amino-acid repeats. These general properties, as well as the presence of a prokaryotic lipoprotein acylation sequence (L-X-Y-C), indicated that the genes encoding V-1 were similar in structure to genes encoding other mycoplasma surface lipoproteins. Further analysis of sequences flanking these genes revealed that these variants arose via an inversion event which provided an interchange of the two variable regions as well as for the conserved region of these genes and immunoblot analyses using rabbit polyclonal antibodies specific for synthetic peptides derived from the sequences of the different variable regions indicated that DNA inversion acted as a switch which allowed only one of the two different genes to be expressed at any given time. This inversion model clearly provides a mechanism by which M. pulmonis can alter its surface architecture and also strongly suggests that the as-yet-undefined function of V-1 residues in the variable carboxy region of these proteins.
虽然肺支原体V-1抗原的变异与该生物体细胞粘附特性的可变表达相关，并且被认为是肺支原体诱导的小鼠呼吸道疾病中的毒力决定因素，但这些抗原的确切功能仍然未知。我们已经克隆并鉴定了来自两个肺支原体UAB CT V-1变体的编码V-1的基因，这两个变体在血细胞吸附特性上有所不同。核苷酸序列比较显示，这两个变体基因在最5'端的724个核苷酸中是相同的。在这个保守区域的3'端发现了含有重复序列的广泛差异区域。根据它们推导的氨基酸序列，一个变体表达了一种94.2 kDa 的V-1蛋白，推测含有40个17个氨基酸的重复序列，另一个变体表达了一种27.4 kDa的蛋白，由2个直接的、不连续的9个氨基酸的重复序列组成。这些一般特性，以及原核脂蛋白酰化序列（L-X-Y-C）的存在，表明编码V-1的基因在结构上与编码其他支原体表面脂蛋白的基因相似。对这些基因侧翼序列的进一步分析表明，这些变体是通过一次倒位事件产生的，该事件导致了两个可变区域以及这些基因的保守区域的互换，并且使用针对来自不同可变区域序列的合成肽的兔多克隆抗体进行的免疫印迹分析表明，DNA倒位起到了开关的作用，使得在任何给定时间只有两个不同基因中的一个能够表达。这种倒位模型清楚地提供了一种机制，通过该机制肺支原体可以改变其表面结构，并且还强烈暗示了这些蛋白质可变羧基区域中V-1残基尚未明确的功能。
