C-terminal domain processing in RgpB from Porphyromonas gingivalis

RgpB belongs to the gingipain group of cysteine proteases from the periodontal pathogen Porphyromonas gingivalis. These proteases have been shown to play a major role in the virulence of the organism. The gingipains along with a number of other virulence factors undergo extensive post-translational modification and exported outside of the cell via a new secretory system. The C-terminal domain (CTD) of these proteins serves to target the passenger domain to the novel secretory pathway. It is unclear, however, whether the CTD also serve to anchor the proteins onto the cell surface. Objectives: To characterise the role the CTD play in RgpB maturation and secretion. Methods: Site-directed mutagenesis was employed to alter specific residues within the CTD to reveal their role in maturation of the RgpB protease. Results: The CTD target newly translated RgpB for maturation and export but is cleaved off the maturing enzyme. The processing site is residue-independent and the site is most likely defined by the local conformation of the region. The length of the site is an important signal for glycosylation of the protein. Conclusion: Maturation of RgpB from Porphyromonas gingivalis is dependent on the cleavage site of the C-terminal domain (CTD). The CTD does not partake in anchorage of the protein to the outer membrane as previously thought but cell anchorage is most likely mediated by post-translational glycosylation of the protein.