Cloning and characterization of two bistructural S-layer-RTX proteins from Campylobacter rectus.
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.
Braun
M
M
Institute for Veterinary Bacteriology, University of Berne, CH-3012 Berne, Switzerland.
Kuhnert
P
P
Nicolet
J
J
Burnens
A P
AP
Frey
J
J
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D001426:Bacterial Proteins; D001427:Bacterial Toxins / Q000235:genetics*; D002167:Campylobacter / Q000235:genetics*; D003001:Cloning, Molecular; D005798:Genes, Bacterial; D008562:Membrane Glycoproteins; D008969:Molecular Sequence Data; D011487:Protein Conformation; D020449:Repetitive Sequences, Amino Acid; D017422:Sequence Analysis, DNA; D013045:Species Specificity
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D008562:Membrane Glycoproteins; C055764:S-layer proteins