Characterizations of peptide binding to SRCRP2 and inhibiting streptococcal adherence

Objective: Previous report showed that the analogue Ssp peptide (A11K) [alanine to lysine at position 11 in the arranged sequence, 1DYQAKLAAYQAEL13] of surface protein adhesions, SspA and SspB from Streptococcus gordonii increased binding to the salivary agglutinin (gp-340/DMBT1) peptide (scavenger receptor cysteine-rich domain 2: SRCRP2) and was homologous to the PAc(365-377) peptide from Streptococcus mutans MT8148. To analyze clearly the function of analogue Ssp peptide in binding and inhibition activity of the peptide to SRCRP2 and streptococcal adherence to saliva coated haydroxyapatite (sHA), we investigated whether an additional substitution by lysine and truncation of peptide influenced the binding of Ssp(A11K) peptide to SRCRP2 and S. mutans binding. Methods: Analogue peptides having substitute lysine at various amino acid positions and truncated peptides were constructed and used for analysis of binding activities to SRCRP2 in BIAcore biosensor and pre-treating sHA. Further, secondary conformations were analyzed using crystallographic analyses using MOE system. Results: Additional substitution peptide, Ssp(A4K-A11K) by lysine at position 4 elevated the binding activities of the Ssp(A11K) peptide to SRCRP2. The distance between positive charged amino acids in the Ssp (A4K-A11K) peptide between 4K and 11K was 12.4 ± 0.2 Å and was close to the distance (11.9 ± 0.0 Å) between the negative charged amino acids, Q and E, on SRCRP2. The molecular angle connecting of positive charged residues, 1D-11K-4K in the Ssp(A4K-A11K) peptide was smaller than the other peptide angles (1D-11K-XK). The inhibition activity of Ssp(A4K-A11K) peptide was higher than Ssp(A11K) peptide, to the binding of S. mutans. The inhibition activity was also observed in the 12-mer truncated peptide (1DYQAKLAAYQAE12) but not the less than 11-mer peptides. Conclusion: Positioning lysine and the 12-mer peptide are important for binding between Ssp peptide and SRCRP2, and the inhibition effect on S. mutans binding to sHA.