Molecular characterization of a Campylobacter jejuni 29-kilodalton periplasmic binding protein

Campylobacter jejuni, a gram-negative, microaerophilic, spiral bacterium, is a common cause of human gastrointestinal disease. Although investigators commonly use C. jejuni glycine-hydrochloride extracts in assays to determine the products that promote the binding of the organism to eukaryotic cells, the proteins contained within these extracts remain ill defined. Characterization of these proteins will provide a better understanding of C. jejuni gene regulation and organization. An antiserum was raised against a C. jejuni 29-kDa gel-purified protein detected in glycine-hydrochloride extracts. This antiserum was used to screen an expression library of C. jejuni. A reactive clone that contained an open reading frame of 256 amino acids was identified. The cloned gene was transcribed and translated, and the product was exported to the periplasmic space in Escherichia coli XL1-Blue. The translated C. jejuni product, designated P29, exhibited significant similarity to the histidine and lysine-arginine-ornithine periplasmic binding proteins (HisJ and LAO, respectively) of Salmonella typhimurium. The C. jejuni gene encoding the P29 protein complemented an S. typhimurium HisJ mutant but not a LAO mutant when provided in trans. These data suggest that the C. jejuni gene encoding the P29 protein is a homolog of the S. typhimurium hisJ gene.