Non-stoichiometric O-acetylation of Shigella flexneri 2a O-specific polysaccharide: synthesis and antigenicity

Abstract

Synthetic functional mimics of the O-antigen from Shigella flexneri 2a are seen as promising vaccine components against endemic shigellosis. Herein, the influence of the polysaccharide non-stoichiometric di-O-acetylation on antigenicity is addressed for the first time. Three decasaccharides, representing relevant internal mono- and di-O-acetylation profiles of the O-antigen, were synthesized from a pivotal protected decasaccharide designed to tailor late stage site-selective O-acetylation. The latter was obtained via a convergent route involving the imidate glycosylation chemistry. Binding studies to five protective mIgGs showed that none of the acetates adds significantly to broad antibody recognition. Yet, one of the five antibodies had a unique pattern of binding. With IC50 in the micromolar to submicromolar range mIgG F22-4 exemplifies a remarkable tight binding antibody against diversely O-acetylated and non-O-acetylated fragments of a neutral polysaccharide of medical importance.

Detailed Investigation of the Immunodominant Role of O‐Antigen Stoichiometric O‐Acetylation as Revealed by Chemical Synthesis, Immunochemistry, Solution Conformation and STD‐NMR Spectroscopy for Shigella flexneri 3a

“…In contrast, other investigations have concluded that O‐acetylation was not essential for protective mAb binding to the SF2a O‐Ag, which is acetylated in a non‐stoichiometric fashion at the OH‐3 A and OH‐6 D groups, the later being shared with the SF3a O‐Ag . Instead, the glucosyl side chain, in this case present within an (E)C branch (α‐ d ‐Glc p ‐(1→4)‐α‐ l ‐Rha p ) as part of the B(E)CD segment, was demonstrated to be critical for binding to five independent protective mIgG .…”

Draft genomes of Shigella strains used by the STOPENTERICS consortium

“…the Generalized Modules for Membrane Antigens (GMMA) approach [ 5 , 6 ]], as well as to improve the immunogenicity of the existing antigens (e.g. synthetic chemistry for glycoconjugates [ 7 ]). To this end, partners of the STOPENTERICS consortium have been integrating basic research, particularly genomics, transcriptomics, proteomics, and other high-throughput technologies, with novel vaccine technologies and synthetic chemistry [ 7 ].…”

“…synthetic chemistry for glycoconjugates [ 7 ]). To this end, partners of the STOPENTERICS consortium have been integrating basic research, particularly genomics, transcriptomics, proteomics, and other high-throughput technologies, with novel vaccine technologies and synthetic chemistry [ 7 ]. To assemble Shigella expertise to identify and rapidly take novel vaccine candidates through to clinical trials for effective vaccine development, the research is carried out among different academic institutions (e.g.…”

Deciphering minimal antigenic epitopes associated with Burkholderia pseudomallei and Burkholderia mallei lipopolysaccharide O-antigens

“…2, the target oligosaccharides would come from five suitably functionalized talose donors ( 8 – 12 ), which are activated at their anomeric position with a trichloroacetimidate (TCA) group 48 . The choice of the TCA group was motivated by the high-yielding coupling reported for structurally similar l -rhamnose donors in the context of the synthesis of bacterial glycans 49 . All of these donors ( 8 – 12 ) were synthesized using a C4 oxidation/reduction sequence from a common allylated rhamnose precursor followed by subsequent regioselective 3-O-methylation or 3-O- para -methoxybenzylation via optimization of the stannylene acetal chemistry 50 (Supplementary Figs.…”