Conformational change of a unique sequence in a fungal galectin from Agrocybe cylindracea controls glycan ligand-binding specificity

Abstract

A fungal galectin from Agrocybe cylindracea (ACG) exhibits broad binding specificity for β-galactose-containing glycans. We determined the crystal structures of wild-type ACG and the N46A mutant, with and without glycan ligands. From these structures and a saccharide-binding analysis of the N46A mutant, we revealed that a conformational change of a unique insertion sequence containing Asn46 provides two binding modes for ACG, and thereby confers broad binding specificity. We propose that the unique sequence provides these two distinct glycan-binding modes by an induced-fit mechanism.

Keywords: A-tetra; ACG; Agrocybe cylindracea galectin; CRD; GalNAcα1–3(Fucα1-2)Galβ1–4GlcNAc; Galectin; Glycan; PEG; Protein engineering; RMSD; Saccharide; X-ray crystallography; carbohydrate recognition domain; polyethylene glycol; root-mean-square deviation.