Jansen R, Briaire J, van Geel A B, Kamp E M, Gielkens A L, Smits M A
Department of Molecular Biology, DLO-Institute for Animal Science and Health (ID-DLO), Lelystad, The Netherlands.
Infect Immun. 1994 Oct;62(10):4411-8. doi: 10.1128/iai.62.10.4411-4418.1994.
Actinobacillus pleuropneumoniae RTX-toxin III (ApxIII) is implicated as an important virulence factor of A. pleuropneumoniae, the causative agent of porcine pleuropneumonia. Recently, the genes coding for ApxIII (apxIIICA) of serotype 8 were cloned and characterized. The toxin appeared to be a member of the RTX-toxin family, as are the other two secreted toxins of A. pleuropneumoniae, i.e., ApxI and ApxII. In this report, we describe the cloning and sequencing of the remaining part of the ApxIII operon of serotype 8. This sequence coded for the RTX secretion proteins ApxIIIB and ApxIIID, which showed 86 and 63% similarity to ApxIB and ApxID, respectively, and 83 and 63% similarity to HlyB and HlyD of Escherichia coli, respectively. Potential functional domains, such as eight transmembrane regions and an ATP-binding cassette, were present in ApxIIIB. We examined the presence of apxIIICABD sequences in the 12 serotypes of A. pleuropneumoniae and found that these sequences were present only in serotypes 2, 3, 4, 6, and 8, the serotypes that secrete ApxIII. Comparison of the apxIIICABD gene sequences of the serotypes revealed very few serotype-specific differences. Only the C terminus of ApxIIIA of serotype 2 differed from ApxIIIA of the other serotypes. The differences were located between the glycine-rich repeats and the secretion signal. The analysis of the apxIIICABD genes completed our efforts to characterize the ApxI, ApxII, and ApxIII operons of the reference strains of the 12 serotypes of A. pleuropneumoniae. We present a complete map of the ApxI, ApxII, and ApxIII operons and discuss this in terms of gene expression and complementation and the role of the toxins in pathogenesis.
胸膜肺炎放线杆菌RTX毒素III（ApxIII）被认为是胸膜肺炎放线杆菌的一种重要毒力因子，胸膜肺炎放线杆菌是猪胸膜肺炎的病原体。最近，8型血清型ApxIII（apxIIICA）的编码基因被克隆并进行了特性分析。该毒素似乎是RTX毒素家族的一员，与胸膜肺炎放线杆菌的其他两种分泌毒素ApxI和ApxII一样。在本报告中，我们描述了8型血清型ApxIII操纵子其余部分的克隆和测序。该序列编码RTX分泌蛋白ApxIIIB和ApxIIID，它们分别与ApxIB和ApxID具有86%和63%的相似性，与大肠杆菌的HlyB和HlyD分别具有83%和63%的相似性。ApxIIIB中存在潜在的功能结构域，如八个跨膜区域和一个ATP结合盒。我们检测了胸膜肺炎放线杆菌12个血清型中apxIIICABD序列的存在情况，发现这些序列仅存在于分泌ApxIII的2型、3型、4型、6型和8型血清型中。血清型的apxIIICABD基因序列比较显示血清型特异性差异很少。只有2型血清型的ApxIIIA的C末端与其他血清型的ApxIIIA不同。差异位于富含甘氨酸的重复序列和分泌信号之间。对apxIIICABD基因的分析完成了我们对胸膜肺炎放线杆菌12个血清型参考菌株的ApxI、ApxII和ApxIII操纵子进行特性分析的工作。我们展示了ApxI、ApxII和ApxIII操纵子的完整图谱，并从基因表达、互补作用以及毒素在发病机制中的作用方面进行了讨论。
