Based on the ‘+2 rule’ for lipoproteins, which relates the final location of a lipoprotein to the amino acid in the

+2 position of the secreted protein [32], the likely cellular location of the Btp zymogens is coupled through a lipid moiety at the post-processing N-terminal Cys residue of the propeptide to the inner leaflet of the outer membrane. They would remain in this inactive form until an activation event occurred. As the proteases would thus have a periplasmic location, for them to contribute to virulence they must come into contact with the host. This could be achieved by a number this website of mechanisms (1) the presence of protease-specific transporters in the outer membrane, (2) by release of the proteases upon bacterial cell death and lysis, or (3) through vesicle-based transport, as previously described for B. fragilis[33]. In the case of the related organism P. gingivalis these vesicles have been associated with proteolytic activity [34, 35]. It is therefore not unlikely that the proteases described in this paper could be exported by vesicles

in a similar manner. The Bti proteins also include predicted leader peptides, and BtiA and BtiB are likely XMU-MP-1 cell line to be lipoproteins, which would also most likely be associated with the outer membrane. BtiZ was not predicted to be a lipoprotein (the signal peptide for BtiZ has a signal peptidase I cleavage site) and it is therefore likely targeted to the periplasm of the Bacteroides cell. Having both membrane associated inhibitor and periplasmic inhibitors may be a strategy for maximizing protection afforded by these inhibitors against the C10 protease activity. Another possibility is that the BtiZ molecule is in the process of accumulating mutations

and becoming non-functional in response to loss of BtpZ activity. We have previously demonstrated the transcriptional 4-Aminobutyrate aminotransferase coupling of B. AZD4547 mouse fragilis C10 protease genes with those for staphostatin-like inhibitors [9]. In the current study transcriptional coupling was also identified for the B. thetaiotaomicron btp and bti genes by Reverse Transcriptase PCR. The btpA gene was found on the same message as btiA. Furthermore, transcriptional coupling was identified for btpB and btiB, and btpZ and btiZ. The btpC gene appears to be transcribed independently of adjacent btp and bti genes. Although, this study does not preclude that the btpA, btpB and btpZ genes could be transcribed independently of the bti genes, the data indicates a similar genetic linkage of these btp genes with staphostatin-like inhibitors as occurs in B. fragilis.