The Treponema denticola outer membrane
lipoprotein-
protease complex (
dentilisin) contributes to
periodontal disease by degrading extracellular matrix components and disrupting intercellular host signaling pathways. We recently demonstrated that prcB, located upstream of and cotranscribed with prcA and prtP, encodes a 22-kDa
lipoprotein that interacts with PrtP and is required for its activity. Here we further characterize products of the
protease locus and their roles in expression, formation, and localization of outer membrane complexes. PrcB migrates in native
gels as part of a >400-kDa complex that includes PrtP and PrcA, as well as the major outer sheath
protein Msp. PrcB is detectable as a minor constituent of the purified active
protease complex, which was previously reported to consist of only PrtP and auxiliary
polypeptides PrcA1 and PrcA2. Though it lacks the canonical ribosome binding site present upstream of both prcA and prtP, PrcB is present at levels similar to those of PrtP in whole-
cell extracts. Immunofluorescence microscopy demonstrated cell surface exposure of the mature forms of PrtP, PrcA1, PrcB, and Msp. The 16-kDa N-terminal acylated fragment of PrtP (predicted to be released during activation of PrtP) was present in
cell extracts but was detected neither in the purified active
protease complex nor on the cell surface. PrcA2, detectable on the surface of Msp-deficient cells but not that of wild-type cells, coimmunoprecipitated with Msp. Our results indicate that PrcB is a component of the outer membrane
lipoprotein protease complex and that Msp and PrcA2 interaction may mediate formation of a very-high-molecular-weight outer membrane complex.