A gene with homology to those encoding an unusual class of C-terminal processing proteases that flanks the invasion-associated locus of has been identified. The 1302 bp gene, termed is located immediately upstream of the gene and encodes a predicted nascent product of 434 amino acids, producing a mature protein of 411 amino acid residues. The CtpA appears to undergo autolysis producing multiple products of 43-46 kDa, and a second group of products of 36-37 kDa. Production of CtpA gives a single product of 41.8 kDa. In addition to a computer-predicted N-terminal secretory signal sequence, the molecular mass difference versus 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 sp. 6803 (69% overall sequence similarity). The mature CtpA protein also has significant homology to the tail-specific protease (Tsp) of 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 gene is conserved in all species examined, as determined by hybridization analyses, but it was not found in or The gene does not directly affect the erythrocyte-invasion phenotype conferred by but its homology to other stress-response processing proteases implies an important role in survival of this intracellular pathogen.


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