文摘
The molecular recognition of polyoxometalates by human serum albumin is studied using two differentpolyoxometalates (POMs) at pH 7.5. The results are compared with those obtained at pH 3.5 and 9.0. At pH7.5, 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, thusindicating a mostly electrostatic binding process. Isothermal titration calorimetry (ITC) experiments showthat 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 bindingbehavior significantly, leading to a simple exothermic process, with several binding sites. Competitive bindingexperiments indicate that the two POMs share one common binding site. In addition, they show the existenceof another important binding site for P5W30. The two POMs exhibit different binding dependences on thepH. The combination of the experimental results with the knowledge of the surface map of the protein in itsN-B conformation transition domain leads to the proposal for the probable binding site of POMs. The presentwork reveals a protein conformation change upon P5W30 binding, a new feature not explicitly documentedin previous studies.