The structure of a Cryptococcus neoformans polysaccharide motif recognized by protective antibodies: A combined NMR and MD study

• 成果类型: Article
• 署名作者: Hargett, Audra A.; Azurmendi, Hugo F.; Crawford, Conor J.; Wear, Maggie P.; Oscarson, Stefan; Casadevall, Arturo; Freedberg, Daron I.
• 署名单位: US Food & Drug Administration (FDA); Center for Biologics Evaluation & Research (CBER); Johns Hopkins University; Johns Hopkins Bloomberg School of Public Health; University College Dublin; Max Planck Society
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-11655
• DOI: 10.1073/pnas.2315733121
• 发表日期: 2024-02-13
• 关键词: chromatography mass-spectrometry; o-deacetylated glucuronoxylomannan; toxoid conjugate vaccine; capsular glucuronoxylomannan; building-blocks; serotype-c; sensitivity; virulence; DYNAMICS; h-1-nmr

摘要

Cryptococcus neoformans is a fungal pathogen responsible for cryptococcosis and cryptococcal meningitis. The C. neoformans' capsular polysaccharide and its shed exopolysaccharide function both as key virulence factors and to protect the fungal cell from phagocytosis. Currently, a glycoconjugate of these polysaccharides is being explored as a vaccine to protect against C. neoformans infection. In this study, NOE andJ-coupling values from NMR experiments were consistent with a converged structure of the synthetic decasaccharide, GXM10-Ac3, calculated from MD simulations. GXM10-Ac3 was designed as an extension of glucuronoxylomannan (GXM) polysaccharide motif (M2) which is common in the clinically predominant serotype A strains and is recognized by protective forms of GXM- specific monoclonal antibodies. The M2 motif is a hexasaccharide with a three- residue alpha-mannan backbone, modified by beta- (1 -> 2)- xyloses (Xyl) on the first two mannoses (Man) and a beta-(1 -> 2)-glucuronic acid (GlcA) on the third Man. Combined NMR and MD analyses reveal that GXM10-Ac3 adopts an extended structure, with Xyl/GlcA branches alternating sides along the alpha-mannan backbone. O- acetyl esters also alternate sides and are grouped in pairs. MD analysis of a twelve M2- repeating unit polymer supports the notion that the GXM10-Ac3 structure is uniformly represented throughout the polysaccharide. This derived GXM model displays high flexibility while maintaining a structural identity, yielding insights to further explore intermolecular interactions between polysaccharides, interactions with anti-GXM mAbs, and the cryptococcal polysaccharide architecture.