Date on Master's Thesis/Doctoral Dissertation

1-2020

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Microbiology and Immunology

Degree Program

Microbiology and Immunology, PhD

Committee Chair

Demuth, Donald

Committee Co-Chair (if applicable)

Lawrenz, Matthew

Committee Member

Alard, Pascale

Committee Member

Potempa, Jan

Committee Member

Graham, James E.

Author's Keywords

Oral biofilm; P. gingivalis; drug discovery

Abstract

Porphyromonas gingivalis is a causative agent of periodontal disease, initially colonizes the oral cavity by adhering to commensal streptococci. Adherence requires the interaction of the minor fimbrial protein (Mfa1) of P. gingivalis with streptococcal antigen I/II (Ag I/II). A peptide derived from Ag I/II peptide has been well characterized and shown to significantly reduce P. gingivalis colonization and bone loss in vivo, suggesting that this interaction represents a potential target for therapeutic intervention. However, the functional motifs of Mfa1 involved in the interaction with Ag I/II remain uncharacterized. A series of N- and C-terminal peptide fragments of Mfa1 were expressed and tested for inhibition of P. gingivalis adherence to S. gordonii. Residues 225-400 of Mfa1 was identified as essential for P. gingivalis adherence. Using the three-dimensional structure of Mfa1, a putative binding cleft was identified and five small-molecule peptidomimetics based on the AgI/II peptide could be docked in this site. Site‐specific mutation of amino acids in the predicted cleft, specifically, R240A, W275A, D321A and A357P inhibited the interaction of Mfa1 with streptococci. Additionally, complementation of an Mfa1‐deficient P. gingivalis strain with wild‐type mfa1 restored adherence to streptococci, whereas complementation with the site‐specific mfa1 mutants resulted in significantly reduced levels of adherence. To develop targeted small molecule inhibitors of this protein-protein interaction, virtual screening was performed to identify compounds that exhibit structural similarity with the two functional motifs (NITVK and VQDLL) of the AgI/II peptide. Thirty-three compounds were tested for in vitro inhibition of P. gingivalis adherence, and the three most potent compounds, N7, N17 and V8, were further characterized. In vivo efficacy of these compounds was evaluated in a murine model of periodontitis. Treatment of mice with each of the compounds reduced P. gingivalis-mediated gingival inflammation as determined by IL-17 expression and significantly reduced maxillary alveolar bone resorption in infected animals. Finally, a series of cytotoxicity tests were performed with human and murine cell lines. N17 and V8 did not show any cytotoxic activity. In summary, we successfully characterized the Mfa1 binding site and identified compounds N17 and V8 as potential lead compounds that will provide the platform to design more potent therapeutic agents that may function to limit or prevent P. gingivalis colonization of the oral cavity.

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