Crocus sativus lectin recognizes Man(3)GlcNAc in the N-glycan core structure

Crocus sativus lectin (CSL) is one of the truly mannose-specific plant lect ins that has a unique binding specificity that sets it apart from others. W e studied sugar-binding specificity of CSL in detail by a solution phase me thod (fluorescence polarization) and three solid phase methods (flow inject ion, surface plasmon resonance, and microtiter plate), using a number of di fferent glycopeptides and oligosaccharides. CSL binds the branched mannotri ose structure in the N-glycan core. Substitution of the terminal Man in the Man alpha(1-3)Man branch with GlcNAc drastically decreases binding affinit y much more than masking of the terminal Man in the Man alpha(l-G)Man branc h, Most interestingly, the beta-Man-linked GlcNAc in N-glycan core structur e contributes greatly to the binding. The effect of this GlcNAc is so stron g that it can substantially offset the negative effect of substitution on t he nonreducing terminal Man residues. On the other hand, the GlcNAc that is usually attached to Asn in N-glycans and the L-FUC linked at the 6-positio n of the GlcNAc are irrelevant to the binding. A bisecting GlcNAc neither c ontributes to nor interferes with the binding. This unique binding specific ity of CSL offers many possibilities of its use in analytical and preparati ve applications.