Unraveling the GM₁specificity 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 towards membranes containing monosialotetrahexosylganglioside (GM 1 ) over disialoganglioside GD 1 a and b) cross-linking of GM 1 ′s by homodimers of Gal-1. We provide evidence about the specificity and the nature of Gal-1 interaction with model membranes containing GM 1 or GD 1 a, employing a broad panel of fluorescence-based and label-free experimental techniques, complemented by atomistic biomolecular simulations. Our study demonstrates that Gal-1 binds indeed specifically to GM 1 , and not to GD 1 a, when embedded in membranes over a wide range of concentrations (i.e., 30 nM to 10 μM). The apparent binding constant is about tens of micromoles. On the other hand, no evidence of Gal-1/GM 1 cross-linking was observed. Our findings suggest that cross-linking does not result from sole interactions between GM1 and Gal-1, indicating that additional triggers are needed in a physiological context, shifting the GM 1 /Gal-1 equilibria towards the membrane-bound homodimeric Gal-1.