Proteome analysis of Madrid E strain of Rickettsia prowazekii

Rickettsia prowazekii, an obligate intracellular Gram-negative bacterium, is the etiologic agent of epidemic typhus. The threat of typhus as a biological weapon lies in its stability in the dried louse feces and in its infection by inhalation of an aerosol. Consequently, it is listed as a select agent and warrants more research to understand its pathogenesis. Although the genomic DNA sequence of strain Madrid E has been completed, the actual expression of the individual protein has not been investigated. In order to provide a global view of the expressed protein profile, the whole cell lysate of purified rickettsia (Madrid E strain) was reduced, alkylated, and digested with trypsin. The total digest was characterized by a two-dimensional liquid chromatography mass spectrometry system and analyzed with a modified version of the ProteomeX workstation. A total of 252 proteins out of 834 predicted protein-coding genes were identified, 238 proteins were identified by the detection of at least two unique peptides. Only 14 proteins were identified by the detection of one unique peptide in all three separate analyses. Among the 238 proteins identified by multiple unique peptides, 230 proteins were found in at least two of three separate analyses. The reproducible and convenient methodology and the information described here have provided a foundation for future proteome study of various R. prowazekii strains with different virulence.