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 (LacNAc II ) 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.

Background:The interleukin-4-inducing principle from Schistosoma mansoni eggs (IPSE/␣-1) triggers basophils to release interleukin-4 and interleukin-13 in an IgE-dependent but antigen-independent way. Results: Structural analysis identified IPSE/␣-1 as a new member of the ␤␥-crystallin superfamily with a unique IgE-binding loop. Conclusion: IPSE/␣-1 activates basophils via IgE-binding crystallin folds. Significance: Schistosomes use unique mechanisms to manipulate the host's immune response.

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