A common binding motif for various bacteria of the bacteria-binding peptide SRCRP2 of DMBT1/gp-340/salivary agglutinin

Abstract

Salivary agglutinin (DMBT1^SAG) is identical to lung glycoprotein-340 and encoded by the deleted in malignant brain tumors-1 gene. It is a member of the scavenger receptor cysteine-rich (SRCR) superfamily, proteins that have one or more SRCR domains. Salivary agglutinin plays a role in oral innate immunity by the binding and agglutination of oral streptococci. Streptococcus mutans has been shown to bind to a 16-mer peptide (QGRVEVLYRGSWGTVC) located within the SRCR domains. Within this peptide, designated SRCR peptide 2, residues VEVL and W are critical for binding. The aim of this study was to investigate binding of DMBT1^SAG to other bacteria. Therefore, interaction between a series of bacteria and DMBT1^SAG, SRCR peptide 2 and its alanine substitution variants was investigated in adhesion and agglutination assays. For different bacteria there was a highly significant correlation between adhesion to DMBT1^SAG and adhesion to SRCR peptide 2, suggesting that SRCR peptide 2 is the major bacteria-binding site. An alanine substitution scan showed that eight amino acids are involved in binding (xRVEVLYxxSWxxxx). The binding motifs varied for different species, but the residues VxVxY and W are always present. In conclusion, a common binding motif (RVEVLYxxxSW) within the SRCR domains is responsible for the broad bacteria-binding spectrum of DMBT1^SAG.