Antigenic properties of the GroEL-like protein of Campylobacter rectus

The purpose of this study was to clarify the antigenic properties of the GroEL‐like protein of Campylobacter rectus using a specific polyclonal antibody directed to the purified 64‐kDa GroEL‐like protein (pAb‐CrGroEL), a polyclonal antibody directed to the Actinobacillus actinomycetemcomitans GroEL‐like protein (pAb‐AaGroEL) and a monoclonal antibody against the recombinant human HSP60 (mAb‐HuHSP60). In SDS‐PAGE/Western immunoblotting analysis, mAb‐HuHSP60, pAb‐CrGroEL and pAb‐AaGroEL were found to react with the GroEL‐like protein (64‐kDa) present in all C. rectus strains. A 150‐kDa protein in C. rectus ATCC 33238 also reacted strongly with pAb‐CrGroEL. This 150‐kDa protein was found to be present on the surface‐associated material of bacterial cells, as determined by transmission electron microscopy and immunogold labelling of cells with pAb‐CrGroEL. Analysis of the first 20 N‐terminal amino acids of the sequence of the 150‐kDa protein revealed a strong homology (80%) with the C. rectus surface layer (S‐layer) protein. Investigation of the biochemical nature of antigenic determinants using periodic acid and proteolytic enzymes showed that the C. rectus GroEL‐like protein possessed immunodominant epitopes in both peptide and carbohydrate chains, and that the immunoreactive determinants of the 150‐kDa protein belonged to carbohydrate. These results suggest that the GroEL‐like protein and the S‐layer protein of C. rectus may share the same carbohydrate epitopes.