The effect of anti-tubercular drug, ethionamide on the secondary structure of serum albumins: A biophysical study

Serum albumin (SA) is the principal extra cellular protein with higher concentration in the blood plasma and acts as a carrier for many drugs to different molecular targets. The present work is designed to investigate the mechanism of interaction between the protein and an anti-tubercular drug, ethionamide (ETH) at the physiological pH by different molecular spectroscopic techniques viz., fluorescence, UV absorption, CD and FTIR. The interaction of SA with ETH was studied by following the quenching of intrinsic fluorescence of protein by ETH at different temperatures. The Stern–Volmer quenching constant, binding constant and the binding site numbers were calculated from fluorescence results. The results indicated the presence of static quenching mechanism in both HSA–ETH and BSA–ETH systems. The distances of separation between the acceptor and donor were calculated based on the theory of fluorescence resonance energy transfer and were found to be 2.35 nm and 2.18 nm for HSA–ETH and BSA–ETH systems, respectively. The conformational changes in protein were confirmed from UV absorption, CD and FTIR spectral data. Displacement experiments with different site probes revealed that the site I was the main binding site for ETH in protein. Effect of some metal ions was also investigated.

► The interaction between ethionamide and serum albumin was investigated by employing simple and different spectroscopic techniques.
► The secondary structure of protein has been changed upon the interaction with ethionamide.
► The fluorescence results indicated the presence of static quenching mechanism in the binding process.
► Site I of the protein is found to be the main binding site for ethionamide.