Unraveling the GM₁ Specificity of Galectin‑1 Binding to Lipid Membranes

Galectin-1 (Gal-1) is a galactose-binding protein involved in various cellular functions. Gal-1's activity has been suggested to be connected to two molecular concepts, which are, however, lacking experimental proof: a) enhanced binding affinity of Gal-1 toward membranes containing monosialotetrahexosylganglioside (GM₁) over disialoganglioside GD₁a and b) cross-linking of GM₁'s by homodimers of Gal-1. We provide evidence about the specificity and the nature of the interaction of Gal-1 with model membranes containing GM₁ or GD₁a, employing a broad panel of fluorescence-based and label-free experimental techniques, complemented by atomistic biomolecular simulations. Our study demonstrates that Gal-1 indeed binds specifically to GM₁ and not to GD₁a when embedded in membranes over a wide range of concentrations (i.e., 30 nM to 20 μM). The apparent binding constant is about tens of micromoles. On the other hand, no evidence of Gal-1/GM₁ cross-linking was observed. Our findings suggest that cross-linking does not result from sole interactions between GM₁ and Gal-1, indicating that in a physiological context, additional triggers are needed, which shift the GM₁/Gal-1 equilibria toward the membrane-bound homodimeric Gal-1.