Interaction of DDP with bovine serum albumin facilitates formation of the protein dimers

Interaction of bovine serum albumin (BSA) with cis- and trans- isomers of diamminedichloroplatinum(II) (DDP) was studied using electrophoretic analysis and Fourier transformed infrared spectroscopy (FTIR). The application of FTIR spectroscopy allowed us to study the DDP/BSA complexes in D2O solutions using protein concentrations close to the physiological level (30 mg/ml) with platinum to BSA molar ratios in the range of 1:1 to 150:1. Under these conditions we have observed formation of relatively weak non-covalent intermolecular protein complexes, which dominated over the BSA-Pt-BSA crosslinks. Analysis of the IR spectra in the region of amide I′ band revealed that the fraction of the α-helical regions in the protein decreases from ∼65% to approximately 55% and 48% in the complexes with cis- and trans-DDP respectively, while the amount of extended β-structures increases from ∼15 to 20% in BSA to 20-30% in its complexes with cis-DDP and up to 35-40% in trans-DDP/BSA complexes. Based on the data obtained we conclude that multiple intermolecular interactions take place in the solution facilitated by the changes in the BSA secondary structure, induced by DDP binding.