Braun M, Kuhnert P, Nicolet J, Burnens A P, Frey J
Institute for Veterinary Bacteriology, University of Berne, CH-3012 Berne, Switzerland.
J Bacteriol. 1999 Apr;181(8):2501-6. doi: 10.1128/JB.181.8.2501-2506.1999.
Campylobacter rectus is an important periodontal pathogen in humans. A surface-layer (S-layer) protein and a cytotoxic activity have been characterized and are thought to be its major virulence factors. The cytotoxic activity was suggested to be due to a pore-forming protein toxin belonging to the RTX (repeats in the structural toxins) family. In the present work, two closely related genes, csxA and csxB (for C. rectus S-layer and RTX protein) were cloned from C. rectus and characterized. The Csx proteins appear to be bifunctional and possess two structurally different domains. The N-terminal part shows similarity with S-layer protein, especially SapA and SapB of C. fetus and Crs of C. rectus. The C-terminal part comprising most of CsxA and CsxB is a domain with 48 and 59 glycine-rich canonical nonapeptide repeats, respectively, arranged in three blocks. Purified recombinant Csx peptides bind Ca2+. These are characteristic traits of RTX toxin proteins. The S-layer and RTX domains of Csx are separated by a proline-rich stretch of 48 amino acids. All C. rectus isolates studied contained copies of either the csxA or csxB gene or both; csx genes were absent from all other Campylobacter and Helicobacter species examined. Serum of a patient with acute gingivitis showed a strong reaction to recombinant Csx protein on immunoblots.
直肠弯曲杆菌是人类重要的牙周病原体。一种表层（S层）蛋白和一种细胞毒性活性已得到表征，被认为是其主要毒力因子。细胞毒性活性被认为是由于一种属于RTX（结构毒素中的重复序列）家族的成孔蛋白毒素所致。在本研究中，从直肠弯曲杆菌中克隆并鉴定了两个密切相关的基因csxA和csxB（分别对应直肠弯曲杆菌的S层蛋白和RTX蛋白）。Csx蛋白似乎具有双功能，拥有两个结构不同的结构域。N端部分与S层蛋白相似，尤其是胎儿弯曲杆菌的SapA和SapB以及直肠弯曲杆菌的Crs。包含大部分CsxA和CsxB的C端部分是一个结构域，分别有48个和59个富含甘氨酸的典型九肽重复序列，排列成三个区域。纯化的重组Csx肽能结合Ca2+。这些是RTX毒素蛋白的特征。Csx的S层和RTX结构域被一段富含脯氨酸的48个氨基酸的序列隔开。所有研究的直肠弯曲杆菌分离株都含有csxA基因或csxB基因的拷贝，或两者都有；在所检测的所有其他弯曲杆菌和螺杆菌物种中均未发现csx基因。一名急性牙龈炎患者的血清在免疫印迹中对重组Csx蛋白显示出强烈反应。
