Identification of an equilibrium intermediate in the unfolding process of galectin-1, which retains its carbohydrate-binding specificity.
The unfolding process of galectin-1 (Gal-1) in the presence of a denaturing agent was examined using fluorescence and far-UV circular dichroism (CD) spectroscopy determinations, and was found to be completely reversible. The data showed that the transitions of guanidine hydrochloride (GdnHCl)-induced lectin unfolding, in the absence of ligand, were biphasic in nature, clearly showing the existence of at least one stable intermediate. On the other hand, the unfolding in the presence of disaccharide yielded data that could fit very well to a two-state model, indicating a stabilizing effect of the ligand. The folding intermediate was further characterized by size exclusion chromatography, near-UV CD and anilinonaphtalene sulfonate binding, and shown to belong to the molten globule type. Strikingly, this intermediate retained its carbohydrate-binding specificity, as evidenced by the tryptophan fluorescence changes detected upon its interaction with lactose.