A gene with homology to those encoding an unusual class of C-terminal processing proteases that flanks the invasion-associated locus ialAB of Bartonella bacilliformis has been identified. The 1302 bp gene, termed ctpA, is located immediately upstream of the ialA gene and encodes a predicted nascent product of 434 amino acids, producing a mature protein of 411 amino acid residues. The Bartonella CtpA appears to undergo autolysis in vitro, producing multiple products of 43-46 kDa, and a second group of products of 36-37 kDa. Production of CtpA in vivo gives a single product of 41.8 kDa. In addition to a computer-predicted N-terminal secretory signal sequence, the molecular mass difference in vivo versus in vitro indicates that CtpA is likely to be secreted and post-translationally modified. The full-length CtpA protein shows 30% identity to the CtpA protein of Synechocystis sp. 6803 (69% overall sequence similarity). The mature CtpA protein also has significant homology to the tail-specific protease (Tsp) of Escherichia coli, with 22% identity and 62% similarity to an internal region of the 660 amino acid Tsp. The CtpA protein does not appear to exhibit haemolysin, collagenase, or caseinase activity. The ctpA gene is conserved in all Bartonella species examined, as determined by hybridization analyses, but it was not found in Brucella abortus or E. coli. The ctpA gene does not directly affect the erythrocyte-invasion phenotype conferred by ialAB, but its homology to other stress-response processing proteases implies an important role in survival of this intracellular pathogen.
- Stress-response protease