New structural insights into the PI‐2 pilus from Streptococcus oralis, an early dental plaque colonizer

Abstract

Streptococcus oralis is a member of the mitis group of oral streptococci and an early colonizer in dental plaque biofilm, a major cause of periodontal disease, dental caries, and other oral infections. S. oralis promotes biofilm growth by coaggregating in a mutualistic partnership with other early colonizers such as Actinomyces oris. For this cell‐to‐cell interaction, A. oris is known to use its sortase‐dependent pilus (type 2), but whether S. oralis uses its PI‐2 (pilus islet 2) pilus is still to be determined. The PI‐2 pilus is predicted to have a heterodimeric structure consisting of two different protein subunits with their own location and function: the tip PitA pilin for adhesion and the backbone PitB pilin for length. Thus far, structural information remains incomplete about the role of PI‐2 pili in the mutualistic mechanism between S. oralis and A. oris. We now report on the crystal structure analysis of PitA and PitB using X‐ray crystallography, small‐angle X‐ray scattering, and molecular docking studies. Accordingly, we propose a structural model for the PI‐2 pilus, wherein repeating PitB subunits are arranged head‐to‐tail to form the long backbone structure with PitA on the outer tip. By performing both in vitro and in vivo experiments, we examined the role played by PitA in mediating the mutualistic interaction between S. oralis and A. oris, which appears to involve the coaggregation factor CafA. We also reveal that the galactose monosaccharide is a conceivable ligand for PitA and thereby might be used to inhibit coaggregation and control oral biofilm development. Database Structural coordinates for the PitA fragment, PitA fragment TbXO4 derivative, full‐length PitA, and PitB from S. oralis have been deposited at the Protein Data Bank as 7VCR, 7W7I, 7VCN, 7W6B, and 7W7I, respectively. Streptococcus pneumoniae PitB coordinates have been deposited as 7F7Y.

Pilus of Streptococcus pneumoniae: structure, function and vaccine potential

“…The structure of PitB (PDB ID: 7F7Y), the backbone pilin, has been resolved to 2.8 Å. It is 110 Å long and 40 Å wide and consists of two domains, D1 and D2 ( Figure 2B ), whose covalent binding is catalyzed by the sortase SrtG1 ( Yadav and Krishnan, 2022 ). The two domains of PitB present an irregular structure; the N-terminal D1 domain consists of 12 chains, and the C-terminal D2 domain consists of 11 chains ( Shaik et al., 2015 ).…”

Oral mitis group streptococci: A silent majority in our oral cavity

“…49 Recently, a structural model for pneumococcal PI-2 pili was proposed using crystal structure analysis, in which repeating PitB subunits were arranged head-to-tail to form a long backbone structure with PitA on the outer tip (Figure 3). 50 A classic study in 1975 reported that some streptococcal strains isolated from human throats produced spreading zones around colonies on blood agar. 101 These strains were identified as "S. sanguis" (oral mitis group), and the spreading growth was caused by twitching motility.…”

“…Recently, a structural model for pneumococcal PI‐2 pili was proposed using crystal structure analysis, in which repeating PitB subunits were arranged head‐to‐tail to form a long backbone structure with PitA on the outer tip (Figure 3). 50 …”

Using Multiplex Polymerase Chain Reaction (m-PCR) Methods to detect six Pathogenic Bacteria in Human Oral Cavity

“…The structural, functional and molecular properties of streptococcal RPS support a recognition role of these cell surface molecules in oral biofilm formation [16,17]. According to research, the cell wall polysaccharides found in S. oralis and other streptococci of the viridans work together as receptors for lectin-like adhesins located on other components of the oral biofilm community [18].…”