Abstract
Porphyromonas gingivalis is associated with chronic periodontitis and may initially colonize the oral cavity by adhering to streptococci. Adhesion to streptococci is driven by interaction of the minor fimbrial antigen (Mfa1) with streptococcal antigen I/II. We identified the region of antigen I/II required for this interaction and developed small molecule mimetics that inhibited P. gingivalis adherence. However, the functional motifs of Mfa1 involved in the interaction with antigen 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. This approach identified residues 225–400 of Mfa1 as essential for P. gingivalis adherence. Using the three‐dimensional structure of Mfa1, a putative binding cleft was identified using SiteMap and five small molecule mimetics could dock in this site. Site‐specific mutation of residues in the predicted cleft, including R240A, W275A, D321A and A357P inhibited the interaction of Mfa1 with streptococci, whereas mutation of residues not in the predicted cleft (V238A, I252F and ΔK253) had no effect. Complementation of an Mfa1‐deficient P. gingivalis strain with wild‐type mfa1 restored adherence to streptococci, whereas complementation with full‐length mfa1 containing the R240A or A357P mutations did not restore adherence. The mutations did not affect polymerization of Mfa1, suggesting that the complemented strains produced intact minor fimbriae. These results identified specific residues and structural motifs required for the Mfa1‐antigen I/II interaction and will facilitate the design of small molecule therapeutics to prevent P. gingivalis colonization of the oral cavity.
Highlights
Periodontal disease is the sixth most prevalent disease in the world and approximately 50% of adults in the United States suffer from some form of periodontitis (Eke, Dye, Wei, Thornton-Evans, & Genco, 2012; Kassebaum et al, 2014)
Gingivalis is strongly associated with chronic adult periodontitis and is an important pathogen that is capable of modulating the host immune response and disrupting normal host/microbe homeostasis (Hajishengallis, 2015; Olsen, Lambris, & Hajishengallis, 2017)
Peptide C280 exhibited reduced activity (~40% inhibition) compared to peptides N279 and N400 but was significantly more active than peptides N194 and N225. These results suggest that essential functional residues that contribute to P. gingivalis adherence to streptococci reside in the region of Mfa1 comprising amino acids 225–400
Summary
Periodontal disease is the sixth most prevalent disease in the world and approximately 50% of adults in the United States suffer from some form of periodontitis (Eke, Dye, Wei, Thornton-Evans, & Genco, 2012; Kassebaum et al, 2014). To determine the functional activity of the truncated Mfa1 polypeptides, S. gordonii cells were pretreated with 1uM of peptide (in PBS) at 25°C for 30 min prior to adding the labeled P. gingivalis.
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