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Molecular dynamics simulations of galectin‐1‐oligosaccharide complexes reveal the molecular basis for ligand diversity

Galectin‐1 is a member of a protein family historically characterized by its ability to bind carbohydrates containing a terminal galactosyl residue. Galectin‐1 is found in a variety of mammalian tissues as a homodimer of 14.5‐kDa subunits. A number of developmental and regulatory processes have been attributed to the ability of galectin‐1 to bind a variety of oligosaccharides containing the Gal‐β‐(1,4)‐GlcNAc (LacNAcII) sequence. To probe the origin of this permissive binding, solvated molecular dynamics (MD) simulations of several representative galectin‐1‐ligand complexes have been performed. Simulations of structurally defined complexes have validated the computational approach and expanded upon data obtained from X‐ray crystallography and surface plasmon resonance measurements. The MD results indicate that a set of anchoring interactions between the galectin‐1 carbohydrate recognition domain (CRD) and the LacNAc core are maintained for a diverse set of ligands and that substituents at the nonreducing terminus of the oligosaccharide extend into the remainder of a characteristic surface groove. The anionic nature of ligands exhibiting relatively high affinities for galectin‐1 implicates electrostatic interactions in ligand selectivity, which is confirmed by a generalized Born analysis of the complexes. The results suggest that the search for a single endogenous ligand or function for this lectin may be inappropriate and instead support a more general role for galectin‐1, in which the lectin is able to crosslink heterogeneous oligosaccharides displayed on a variety of cell surfaces. Such binding promiscuity provides an explanation for the variety of adhesion phenomena mediated by galectin‐1. Proteins 2003. © 2003 Wiley‐Liss, Inc.