A glycoside analog of mammalian oligomannose formulated with a TLR4-stimulating adjuvant elicits HIV-1 cross-reactive antibodies

Mechanisms of interactions in pattern-recognition of common glycostructures across pectin-derived heteropolysaccharides by Toll-like receptor 4

Complex pectin, originating from terrestrial plant cell walls has been attracting research attention as a promising source of a new innate immune modulator. Numerous bioactive polysaccharides associated with pectin are newly reported every year, but the general mechanism of their immunological action remains unclear owing to the complexity and heterogeneity of pectin. Herein, we systematically investigated the interactions in pattern-recognition for common glycostructures of pectic heteropolysaccharides (HPSs) by Toll-like receptors (TLRs). The compositional similarity of glycosyl residues derived from pectic HPS was confirmed by conducting systematic reviews, leading to molecular modeling of representative pectic segments. Via structural investigation, the inner concavity of leucine-rich repeats of TLR4 was predicted to act as a binding motif for carbohydrate recognition, and subsequent simulations predicted the binding modes and conformations. We experimentally demonstrated that pectic HPS exhibits the non-canonical and multivalent binding aspects for TLR4 resulting in receptor activation. Furthermore, we showed that pectic HPSs were selectively clustered with TLR4 during endocytosis, inducing downstream signals to cause phenotypic activation of macrophages. Overall, we have presented a better explanation for the pattern recognition of pectic HPS and further proposed an approach to understand the interaction between complex carbohydrates and proteins.

Synthetic neoglycoconjugates of hepta- and nonamannoside ligands for eliciting oligomannose-specific HIV-1-neutralizing antibodies

Oligomannose-type glycans on the spike protein of HIV-1 constitute relevant epitopes to elicit broadly neutralizing antibodies (bnAbs). Herein we describe an improved synthesis of α- and β-linked hepta- and nonamannosyl ligands that, subsequently, were converted into BSA and CRM 197 neoglycoconjugates. We assembled the ligands from anomeric 3-azidopropyl spacer glycosides from select 3-O-protected thiocresyl mannoside donors. Chain extensions were achieved using 4+3 or 4+5 block synthesis of thiocresyl and trichloroacetimidate glycosyl donors. Subsequent global deprotection generated the 3-aminopropyl oligosaccharide ligands. ELISA binding data obtained with the β-anomeric hepta- and nonamannosyl conjugates with a selection of HIV-1 bnAbs showed comparable binding of both mannosyl ligands by Fab fragments yet lesser binding of the nonasaccharide conjugate by the corresponding IgG antibodies. These results support previous observations that a complete Man 9 structure might not be the preferred antigenic binding motif for some oligomannose-specific antibodies and have implications for glycoside designs to elicit oligomannose-targeted HIV-1-neutralizing antibodies.