A carboxy-terminal processing protease gene is located immediately upstream of the invasion-associated locus from Bartonella bacilliformis

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Abstract
A gene with homology to those encoding an unusual class of C-terminal processing proteases that flanks the invasion-associated locusiaIABofBartonella bacilliformishas been identified. The 1302 bp gene, termedctpA,is located immediately upstream of theialAgene and encodes a predicted nascent product of 434 amino acids, producing a mature protein of 411 amino acid residues. TheBartonellaCtpA appears to undergo autolysisin vitro,producing multiple products of 43-46 kDa, and a second group of products of 36-37 kDa. Production of CtpAin vivogives a single product of 41.8 kDa. In addition to a computer-predicted N-terminal secretory signal sequence, the molecular mass differencein vivoversusin vitroindicates that CtpA is likely to be secreted and post-translationally modified. The full-length CtpA protein shows 30% identity to the CtpA protein ofSynechocystissp. 6803 (69% overall sequence similarity). The mature CtpA protein also has significant homology to the tail-specific protease (Tsp) ofEscherichia 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. ThectpAgene is conserved in allBartonellaspecies examined, as determined by hybridization analyses, but it was not found inBrucella abortusorE. coli.ThectpAgene does not directly affect the erythrocyte-invasion phenotype conferred byiaIAB,but its homology to other stress-response processing proteases implies an important role in survival of this intracellular pathogen.