Nucleotide sequence of the gene and features of the major outer membrane protein of a virulent Rickettsia prowazekii strain.

We have determined the nucleotide sequence of the gene for a major outer membrane protein (MOMP) of apparent molecular weight 29.5 kD of the virulent Breinl strain of Rickettsia prowazekii. The gene contains an open reading frame (ORF) that encodes a 282-amino-acid polypeptide with a calculated molecular mass of 31549 daltons. A signal-like peptide sequence is found at the deduced N terminus. A heterologous 29.5-kD antigen expressed in Escherichia coli was shown to be secreted into the periplasm. A database search for similar protein sequences revealed considerable homology of the polypeptide with the E. coli peptidyl-prolyl cis/trans isomerase and related proteins of the parvulin family. The genes for MOMP of the virulent Breinl and EVir strains and the vaccine Madrid E strain were amplified using specific primers and cloned into expression vector pQE-30. We found that the polypeptides encoded by the recombinant DNAs do not differ in SDS-PAGE mobility, while the native MOMP of the Breinl strain is known to be different from the corresponding proteins of the Madrid E and EVir strains. Furthermore, no differences within the ORF for the 29.5-kD proteins of the three strains were found by restriction endonuclease analysis of polymerase chain reaction (PCR) products. A possible role of parvulin-like protein (Plp) in the virulence of epidemic typhus agent and the nature of interstrain differences are discussed. Near the plp gene on the opposite strand, an origin of the gene that codes for the SecA subunit of a preprotein translocase was found.