Purification, characterization and sequence analysis of Omp50, a new porinisolated from Campylobacter jejuni

A novel pore-forming protein identified in Campylobacter was purified by io n-exchange chromatography and named Omp50 according to both its molecular m ass and its outer membrane localization. We observed a pore-forming ability of Omp50 after re-incorporation into artificial membranes. The protein ind uced cation-selective channels with major conductance values of 50-60 pS in 1 M NaCl. N-terminal sequencing allowed us to identify the predicted codin g sequence Cj1170c from the Campylobacter jejuni genome database as the cor responding gene in the NCTC 11168 genome sequence. The gene, designated omp 50, consists of a 1425 bp open reading frame encoding a deduced 453-amino a cid protein with a calculated pI of 5.81 and a molecular mass of 51169.2 Da . The protein possessed a 20-amino acid leader sequence. No significant sim ilarity was found between Omp50 and porin protein sequences already determi ned. Moreover, the protein showed only weak sequence identity with the majo r outer-membrane protein (MOMP) of Campylobacter, correlating with the abse nce of antigenic cross-reactivity between these two proteins. Omp50 is expr essed in C. jejuni and Campylobacter lari but not in Campylobacter coli. Th e gene, however, was detected in all three species by PCR. According to its conformation and functional properties, the protein would belong to the fa mily of outer-membrane monomeric porins.