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-1s 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 (GM1) over disialoganglioside GD1a and b) cross-linking of GM1s by homodimers of Gal-1. We provide evidence about the specificity and the nature of Gal-1 interaction 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 binds indeed specifically to GM1, and not to GD1a, when embedded in membranes over a wide range of concentrations (i.e., 30 nM to 10 M). 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 towards the membrane-bound homodimeric Gal-1. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=198 SRC="FIGDIR/small/614102v2_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@c4ff01org.highwire.dtl.DTLVardef@141c82eorg.highwire.dtl.DTLVardef@1bd7c0borg.highwire.dtl.DTLVardef@11af49e_HPS_FORMAT_FIGEXP M_FIG C_FIG