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Chemoenzymatic Synthesis of N-glycan Positional Isomers and Evidence for Branch Selective Binding by Monoclonal Antibodies and Human C-type Lectin Receptors

Begoña Echeverria, Sonia Serna, Silvia Achilli, Corinne Vivès, Julie Pham, Michel Thépaut, Cornelis H. Hokke, Franck Fieschi, Niels-Christian Reichardt

ACS Chem Biol, 2018, 13 (8), 2269-2279

Here, we describe a strategy for the rapid preparation of pure positional isomers of complex N-glycans to complement an existing array comprising a larger number of Nglycans and smaller glycan structures. The expanded array was then employed to study context-dependent binding of structural glycan fragments by monoclonal antibodies and C-type lectins. A partial enzymatic elongation of semiprotected core structures was combined with the protecting-group-aided separation of positional isomers by preparative HPLC. This methodology, which avoids the laborious chemical differentiation of antennae, was employed for the preparation of eight biantennary N-glycans with Galβ1,4GlcNAc (LN), GalNAcβ1,4GlcNAc (LDN), and GalNAcβ1,4-[Fucα1,3]GlcNAc (LDNF) motifs presented on either one or both antennae. Screening of the binding specificities of three anti-LeX monoclonal IgM antibodies raised against S. mansoni glycans and three C-type lectin receptors of the innate immune system, namely DC-SIGN, DC-SIGNR, and LSECtin, revealed a surprising context-dependent fine specificity for the recognition of the glycan motifs. Moreover, we observed a striking selection of one individual positional isomer over the other by the C-type lectins tested, underscoring the biological relevance of the structural context of glycan elements in molecular
recognition.