Interaction of cisplatin drug with Na,K-ATPase: drug binding mode and protein secondary structure

cis-Pt(NH,)(2)Cl-2 (cisplatin) is an antitumor drug with many severe toxic side effects including enzymatic changes associated with its mechanism of a ction. This study was designed to examine the interaction of cisplatin drug with the Na+, K+-dependent adenosine triphosphatase (Na,K-ATPase) in H2O a nd D2O solutions at physiological pH, using drug concentrations of 0.1 muM to 1 mM. UV absorption spectra and Fourier transform infrared difference sp ectroscopy with its self-deconvolution, second derivative resolution enhanc ement and curve-fitting procedures were applied to characterize the drug bi nding mode, the drug binding constant and the protein secondary structure i n the cisplatin-ATPase complexes. Spectroscopic evidence showed that at low drug concentration (0.1 muM), cisplatin binds mainly to the lipid portion of the enzyme, whereas at higher drug contents, the Pt cation interaction i s through the polypeptide C=O and C-N groups with overall binding constant of K=1.93x10(4) M-1. At high cisplatin concentration (1 mM), drug binding r esults in protein secondary structural changes from that of the alpha -heli x 19.8%; beta -pleated 25.6%; turn 9.1%; beta -antiparallel 7.5% and random 38%, in the free Na,K-ATPase to that of the alpha -helix 22.2%; beta -plea ted 23.2%; turn 9.4%; beta -antiparallel 2.2% and random 43%, in the cis-Pt -ATPase complexes. (C) 2001 Elsevier Science BY All rights reserved.