DESCRIPTION: The predominance of spirochetes in subgingival plaque associated with severe periodontal lesions suggests an important role in periodontal pathogenesis. The goal of this research is to characterize interactions of Treponema denticola with subgingival tissues at the molecular level. By focusing on analysis of surface-expressed proteins that directly affect host cells, insights will be gained into mechanisms of periodontal cytopathology. The major outer membrane protein (Msp) of T. denticola binds to cells and ECM components, and has pore-forming cytotoxic activity. Msp is genetically conserved in many oral spirochetes, yet shows considerable inter-strain heterogeneity, suggesting that it is an important immunogen. The overall hypothesis is that Msp is a significant virulence determinant in periodontal disease, and is a key component of an outer membrane protein complex mediating interactions of the spirochete with subgingival tissue. Specific Aims of the proposed research, and the individual hypotheses to be tested are: 1) to characterize T. denticola proteins associated with Msp expression. Outer membrane components other than Msp are required for native Msp expression and assembly of the native outer membrane complex. Isogenic mutants and recombinant expression systems will be used to characterize these processes. 2) to identify immunodominant and functional domains of Msp. Antigenic heterogeneity of Msp is a factor in host antibody recognition of oral spirochetes. Archived serum samples will be screened for reactivity with specific Msps. Genes encoding novel Msps will be identified in patient plaque samples. 3) to characterize the role of Msp in cytopathic cellular responses to T. denticola. The ability of parent and msp mutant strains to bind host cells, ECM and serum components, and to activate pro-inflammatory cellular responses will be assayed. A putative Msp receptor identified on epithelial cell surfaces will be characterized. These studies, which involve both genetic and biochemical analyses, are intended to contribute significantly to the understanding of microbe-host interactions in the etiology of periodontal diseases, and to basic knowledge of the molecular biology of pathogenic spirochetes.