Measuring the binding affinity for proteins that can aggregate or undergo complex binding motifs presents a variety of challenges. In this study, fluorescence lifetime measurements using intrinsic tryptophan fluorescence were performed to address these challenges and to quantify the binding of a series of carbohydrates and carbohydrate-functionalized dendrimers to recombinant human galectin-3. Collectively, galectins represent an important target for study; in particular, galectin-3 plays a variety of roles in cancer biology. Galectin-3 binding dissociation constants (K D) were quantified: lactoside (73 ± 4 μM), methyllactoside (54 ± 10 μM), and lactoside-functionalized G(2), G(4), and G(6)-PAMAM dendrimers (120 ± 58 μM, 100 ± 45 μM, and 130 ± 25 μM, respectively). The chosen examples showcase the widespread utility of time-dependent fluorescence spectroscopy for determining binding constants, including interactions for which standard methods have significant limitations.
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