Interaction of AZT with human serum albumin studied by capillary electrophoresis, FTIR and CD spectroscopic methods.

The thymidine analog 3'-azido-3'-deoxythymidine (AZT) is still one of the effective drugs against human immunodeficiency (HIV) infection. AZT has been used as inhibitor of HIV-1 reverse transcriptase, the virus encoded enzyme which catalyzes transcription of viral RNA to DNA. The drug interaction with protein has been included in its mechanism of action. Human serum albumin (HSA) is a carrier of many drugs in vivo and thus AZT-HSA complexation can serve as a model for drug-protein interaction. This study was designed to examine the interaction of AZT with human serum albumin at physiological conditions using constant protein concentration (0.2% or 2%) and different drug contents (5 to 1000 microM). Capillary electrophoresis, FTIR and CD spectroscopic methods were used to determine the drug binding mode, the drug binding constant and the effects of drug-HSA complexation on the protein and AZT conformations in aqueous solution. Capillary electrophoresis and spectroscopic results showed two major bindings for the AZT-HSA complexes with K(1)=1.9 x 10(6) M(-1)and K(2)= 2.1 x 10(4) M(-1). Minor alterations of the protein secondary structure from that of the alpha-helix to beta-sheet were observed upon drug complexation, whereas the drug sugar pucker remained in the C2'-endo/anti conformation upon protein interaction.