Minimal epitope for Mannitou IgM on paucimannose-carrying glycoproteins

Stefania Robakiewicz, Clarisse Bridot, Sonia Serna, Ana Gimeno, Begoña Echeverria, Sandra Delgado, Jérôme Ruyck, Shubham Semwal, Diego Charro, Ann Dansercoer, Kenneth Verstraete, Mikel Azkargorta, Kim Noort, Ruud Wilbers, Savvas N. Savvides, Nicola G.A. Abrescia, Ana Arda, Niels C. Reichardt*, Jesús Jiménez-Barbero*, Julie Bouckaert*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

3 Citations (Scopus)


Paucimannosidic glycans are restricted to the core structure [Man1–3GlcNAc2Fuc0–1] of N-glycans and are rarely found in mammalian tissues. Yet, especially [Man2-3GlcNAc2Fuc1] have been found significantly upregulated in tumors, including in colorectal and liver cancer. Mannitou IgM is a murine monoclonal antibody that was previously shown to recognise Man3GlcNAc2 with an almost exclusive selectivity. Here, we have sought the definition of the minimal glycan epitope of Mannitou IgM, initiated by screening on a newly designed paucimannosidic glycan microarray. Among the best binders were Man3GlcNAc2 and its α1,6 core-fucosylated variant, Man3GlcNAc2Fuc1. Unexpectedly and in contrast to earlier findings, Man5GlcNAc2-type structures bind equally well and a large tolerance was observed for substitutions on the α1,6 arm. It was confirmed that any substitution on the single α1,3-linked mannose completely abolishes binding. Surface plasmon resonance for kinetic measurements of Mannitou IgM binding, either directly on the glycans or as presented on omega-1 and kappa-5 soluble egg antigens from the helminth parasite Schistosoma mansoni, showed submicromolar affinities. To characterize the epitope in greater and atomic detail, saturation transfer difference nuclear magnetic resonance spectroscopy was performed with the Mannitou antigen-binding fragment. The STD-NMR data demonstrated the strongest interactions with the aliphatic protons H1 and H2 of the α1–3-linked mannose, and weaker imprints on its H3, H4 and H5 protons. In conclusion, Mannitou IgM binding requires a non-substituted α1,3-linked mannose branch of paucimannose also on proteins, making it a highly specific tool for the distinction of concurrent human tumor-associated carbohydrate antigens.
Original languageEnglish
Article numbercwab027
Pages (from-to)1005-1017
Issue number8
Early online date28 Apr 2021
Publication statusPublished - 2021


  • core fucose
  • IgM
  • Mannitou
  • N-glycan
  • paucimannosidic epitopes


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