Saccharide binding by intelectins.

This communication probes ligand binding by human Intelectin-1 with several saccharides. Human Intelectin-1 was previously reported to bind to microbial glycans via ribofuranoside or galactofuranoside residues, whereas subsequently, a crystal structure of ligand bound hITLN1 indicated that hITLN1 does not bind to ribofuranoside but distinguishes between microbial and human glycans through a glycan motif - a terminal, acyclic 1,2-diol, which is present on galactofuranose and other microbial saccharides. Here, we demonstrate that besides glycerol and glycerol derivatives (which have an acyclic 1,2-diol), and 2-deoxy-d-galactose, d-ribose and 2-deoxy-d-ribose, which have been previously reported as human Intelectin-1 ligands, 2-C-hydroxymethyl-d-ribose, d-talose, d-idose, d-altrose and sorbitol also elute human Intelectin-1 from Sepharose CL-6B. Interestingly, Sepharose, 2-deoxy-d-galactose (in its pyranose form), 2-C-hydroxymethyl-d-ribose, d-ribose and 2-deoxy d-ribose lack a terminal, acyclic 1,2-diol. We discuss the implications of these observations and rationalize the discrepancies in the apparent affinity of saccharide ligands for hITLN1 with different assay formats. We also report the distinct saccharide binding profiles of the hITLN1 homologues, HaloITLN and XL35ITLN, and demonstrate that hITLN1 binding to a saccharide ligand may modulate binding to its protein ligand, lactoferrin and vice versa.