IMMUNOCHEMICAL STRUCTURE OF THE OMPD PORIN FROM SALMONELLA-TYPHIMURIUM

The OmpD porin was isolated and purified from Salmonella typhimurium s train SH 7454 (ompC::Tn10), digested with cyanogen bromide (CNBr) and the peptide fragments were separated by SDS-PAGE. N-terminal sequencin g identified a total of 96 residues from four distinct peptides. The s equence showed that OmpD is homologous to NmpC (75% identity), Lc (75% ) and OmpC (70%) from Escherichia coli, and OmpC (68%) from S. typhimu rium. The sequence was essentially identical to the translated sequenc e of an nmpC-like gene of S. typhimurium, currently placed at 38.6 cen tisomes of the chromosome. Our results and other data suggest, however , that this gene is actually the ompD gene, which is more correctly pl aced in the 34 centisome region of the chromosome. The CNBr-generated peptides were also screened with 16 anti-S. typhimurium OmpD monoclona l antibodies by Western blotting. These results, in conjunction with t he prediction of the OmpD folding pattern based on the known three-dim ensional structure of E. coli OmpF, showed a close immunological relat ionship among S. typhimurium OmpD and E. coli NmpC and Lc, and a stron g conservation of sequences within the transmembrane beta strands of t hese porins and E. coli OmpC, PhoE and OmpF, and Salmonella typhi OmpC .