Isolation of galectin-1 from human platelets: its interaction with actin.

Galectins are a family of animal lectins defined by their β-galactoside-binding specificity and a consensus sequence in their carbohydrate-recognition domain. Galectin-1 (Gal-1) is expressed as a non-covalently linked homodimer present in a variety of tissues. Here we describe its isolation from human platelets by a procedure involving ionic exchange chromatography and affinity chromatography on lactose-agarose. Platelet Gal-1 co-purifies with actin, forming an actin-Gal-1 complex which does no dissociate even after treatment with sodium dodecyl sulfate. The presence of both proteins was confirmed by Western blot and by trypsin digestion followed by mass spectrometry identification. By hemagglutination assays we studied the response of recombinant Gal-1/actin, mixed and pre-incubated in different proportions, and then tested against neuraminidase treated rabbit red blood cells. The complex formation was confirmed by confocal microscopy, showing that both proteins co-localised in resting platelets as well as in thrombin-activated ones. These results suggest that endogenous Gal-1 forms an intracellular complex with monomeric actin and that, after platelet activation, Gal-1 could play a role in the polymerization-depolymerization process of actin, which concludes in platelet aggregation.