Evaluation of the interaction of levothyroxine with bovine serum albumin using spectroscopic and molecular docking studies

Abstract

Bovine serum albumin (BSA) acts as a carrier for many endogenous and exogenous compounds, such as thyroid hormones or corresponding drugs. Binding of the hydrophilic levothyroxine drug (LT4) to BSA is of significant pharmacological importance. In this work, UV-vis measurements were used to determine the pH value at which LT4 interacts optimally with proteins. The binding mechanism and affinity of the interaction between LT4 and BSA were investigated using Fourier-transform infrared spectroscopy (FT-IR), fluorescence, fluorescence resonance energy transfer (FRET), Surface Plasmon Resonance (SPR), supplemented by molecular docking analysis. Fluorescence measurements revealed the quenching effect of LT4 on the BSA intrinsic fluorescence and LT4 binding with BSA is driven by a ground-state complex formation that may be accompanied by a nonradiative energy transfer process. The thermodynamic parameters correspond to an enthalpic process, driven mainly by hydrogen bonds and van der Waals forces. Using SPR, the adsorbed amount of biomolecules was calculated and the binding affinity of LT4 with confined-BSA was characterized, indicating that the BSA immobilization plays an important role in LT4 binding. Docking studies confirmed the formation of the LT4-BSA complex with LT4 bound to site I on the BSA structure mainly with amino acid residues Trp 213, Tyr 137, Tyr 147. The calculation of the apparent association constant confirms the result obtained in SPR.

Communicated by Ramaswamy H. Sarma

Keywords:

• Interaction
• fluorescence
• FRET
• FT-IR
• SPR
• molecular docking

Acknowledgements

The authors are very much indebted to Professor Dr. Aurel Popescu, for very helpful suggestions and permanent encouragement.

Additional information

Funding

This work was supported by a grant of the Ministerul Cercetării şi Inovării, CCCDI - UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0062, contract no. 58, within PNCDI III and the structural funds project PRO-DD (POS-CCE, O.2.2.1., ID 123, SMIS 2637, No 11/2009) for providing some of the infrastructure used in this work.