The binding mechanism ofStreptococcus suisaccessory virulence factor and adhesin SadP to globotetraosylceramide

AbstractStreptococcus suisis part of the pig commensal microbiome and a major pathogen causing pneumonia and meningitis in pigs and occasionally also zoonotic meningitis. According to genomic analysis,S. suisis divided into asymptomatic carriage, respiratory and systemic strains with distinct genomic signatures. The virulence factorS. suisadhesin P (SadP) recognizes the galabiose Galα1–4Gal-oligosaccharide. Based on its oligosaccharide fine specificity, SadP can be divided into subtypes PNand PO. We show here that subtype PNis distributed in the systemic strains that cause meningitis, whereas type POis found in asymptomatic carriage and respiratory strains. Both types of SadP are shown to predominantly bind to pig lung globotriaosylceramide (Gb3). However, SadP adhesin from systemic subtype PNstrain also binds to globotetraosylceramide (Gb4). Mutagenesis studies of the galabiose-binding domain of type PNSadP adhesin showed that the amino acid asparagine-285, which is replaced by an aspartate residue in type Po SadP, was required for binding to Gb4 and, strikingly, it was also required for interaction with the glycomimetic inhibitor phenylurea-galabiose. Molecular dynamics simulations provided further insight into the role of Asn-285 for Gb4 and phenylurea-galabiose binding, suggesting additional hydrogen bonding to terminal GalNAc of Gb4 and urea-group. Thus, the Asn-285-mediated molecular mechanism of type PNSadP binding to Gb4 could be used as a candidate to selectively targetS. suisin invasive systemic disease without interfering with commensal strains, which may open up new venues for developing intervention strategies against this pathogen.