Wang B, Kraig E, Kolodrubetz D
Department of Microbiology, University of Texas Health Science Center, San Antonio 78284, USA.
Infect Immun. 1998 Apr;66(4):1521-6. doi: 10.1128/IAI.66.4.1521-1526.1998.
Strains of the periodontal pathogen Campylobacter rectus express a 150- to 166-kDa protein on their cell surface. This protein forms a paracrystalline lattice, called the surface layer (S-layer), on the outer membrane of this gram-negative bacterium. To initiate a genetic analysis of the function of the S-layer in the pathogenesis of C. rectus, we have cloned and characterized its gene. The S-layer gene (crs) from C. rectus 314 encodes a cell surface protein which does not have a cleaved signal peptide at its amino terminus. Although the amino acid sequence deduced from the crs gene has 50% identity with the amino-terminal 30 amino acids of the four S-layer proteins from Campylobacter fetus, the similarity decreases to less than 16% over the rest of the protein. Thus, the crs gene from C. rectus encodes a novel S-layer protein whose precise role in pathogenesis may differ from that of S-layer proteins from other organisms. Southern and Northern blot analyses with probes from different segments of the crs gene indicate that the S-layer gene is a single-copy, monocistronic gene in C. rectus. RNA end mapping and sequence analyses were used to define the crs promoter; there is an exact match to the Escherichia coli -10 promoter consensus sequence but only a weak match to the -35 consensus element. Southern blots of DNA from another strain of C. rectus, ATCC 33238, demonstrated that the crs gene is also present in that strain but that there are numerous restriction fragment length polymorphisms in the second half of the gene. This finding suggests that the carboxy halves of the S-layer proteins from strains 314 and 33238 differ. It remains to be determined whether the diversities in sequence are reflected in functional or antigenic differences important for the pathogenesis of different C. rectus isolates.
牙周病原体直肠弯曲杆菌菌株在其细胞表面表达一种150至166千道尔顿的蛋白质。这种蛋白质在这种革兰氏阴性细菌的外膜上形成一种称为表层（S层）的准晶体晶格。为了启动对S层在直肠弯曲杆菌致病机制中功能的遗传分析，我们克隆并鉴定了其基因。来自直肠弯曲杆菌314的S层基因（crs）编码一种细胞表面蛋白，该蛋白在其氨基末端没有切割的信号肽。尽管从crs基因推导的氨基酸序列与胎儿弯曲杆菌四种S层蛋白的氨基末端30个氨基酸有50%的同一性，但在该蛋白的其余部分相似性降至不到16%。因此，直肠弯曲杆菌的crs基因编码一种新型的S层蛋白，其在致病机制中的精确作用可能与其他生物体的S层蛋白不同。用来自crs基因不同片段的探针进行的Southern和Northern印迹分析表明，S层基因在直肠弯曲杆菌中是单拷贝、单顺反子基因。RNA末端图谱和序列分析用于确定crs启动子；与大肠杆菌-10启动子共有序列完全匹配，但与-35共有元件只有微弱匹配。来自另一株直肠弯曲杆菌ATCC 33238的DNA的Southern印迹表明，crs基因也存在于该菌株中，但该基因后半部分有许多限制性片段长度多态性。这一发现表明，314和33238菌株的S层蛋白的羧基末端不同。序列差异是否反映在对不同直肠弯曲杆菌分离株致病机制重要的功能或抗原差异中，仍有待确定。
