Rickettsia rickettsii str. Iowa Genome sequencing and assembly. Rickettsia rickettsii str. Iowa

Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, contains two immunodominant proteins, rOmpA and rOmpB, in the outer membrane. Both rOmpA and rOmpB are conserved throughout spotted fever group rickettsiae as members of a family of autotransporter proteins. Previously, it was demonstrated that rOmpB is proteolytically processed with the cleavage site residing near the autotransporter domain at the carboxy-terminal end of the protein, cleaving the 168 kDa precursor into apparent 120 kDa and 32 kDa fragments. The 120 and 32 kDa fragments remain non-covalently associated on the surface of the bacterium with implications that the 32kDa fragment functions as the membrane anchor domain. Here we present evidence for a similar post-translational processing of rOmpA. rOmpA is expressed as a predicted 224 kDa precursor yet is observed on SDS-PAGE as a 190 kDa protein. A small rOmpA fragment of ~32kDa was discovered during surface proteome analysis and identified as the carboxy terminal end of the protein. A rabbit polyclonal antibody was generated to the autotransporter region of rOmpA and confirmed a 32kDa fragment corresponding to the calculated mass of a proteolytically cleaved rOmpA autotransporter region. N-terminal amino acid sequencing revealed a cleavage site on the carboxy-terminal side of Ser-1958 in rOmpA. An avirulent strain of R. rickettsii Iowa deficient in rOmpB processing was also defective in processing of rOmpA. The similarities of the cleavage sites and failure of R. rickettsii Iowa to process either rOmpA or rOmpB suggest a single enzyme may be responsible for both processing events.