Polyoxometalate binding to human serum albumin: a thermodynamic and spectroscopic approach.

TLDR: The present work reveals a protein conformation change upon P5W30 binding, a new feature not explicitly documented in previous studies, which is a simple exothermic process, with several binding sites.

Abstract: The molecular recognition of polyoxometalates by human serum albumin is studied using two different polyoxometalates (POMs) at pH 7.5. The results are compared with those obtained at pH 3.5 and 9.0. At pH 7.5, both POMs strongly interact with the protein with different binding behaviors. The Keggin shaped POM, [H2W12O40]6- (H2W12), specifically binds the protein, forming a complex with a 1:1 stoichiometry with Ka = 2.9 × 106 M-1. The binding constant decreased dramatically with the increase of the ionic strength, thus indicating a mostly electrostatic binding process. Isothermal titration calorimetry (ITC) experiments show that the binding is an enthalpically driven exothermic process. For the wheel shaped POM [NaP5W30O110]14- (P5W30), there are up to five binding sites on the protein. Increasing the ionic strength changes the binding behavior significantly, leading to a simple exothermic process, with several binding sites. Competitive binding experiments indicate that the two POMs share one common bindi...