Spectroscopic investigation and molecular docking analysis of an FRET probe: Trypsin from bovine pancreas@Coumarin 440 dye conjugate

Abstract

Herein, a systematic investigation of energy transfer from bovine pancreas trypsin to coumarin 440 (C440) dye is presented with an aim to design a FRET probe, as trypsin is an important enzyme for absorption and digestion of nutrients in the small intestine. Conformational changes in trypsin upon interaction with C440 dye are studied by employing both spectroscopic and molecular docking techniques. Steady state and time resolved measurements validate the formation of trypsin-C440 complex via dynamic quenching, that confirms the role of C440 as an inhibitor to suppress the activity of trypsin. Spectral overlap integral, Förster's distance, rate and energy transfer efficiency are calculated from steady state measurements. The observed blue shift in fluorescence suggests conformational changes due to hydrophobicity that arises in trypsin structure on binding with C440 possibly due to their interaction through H-bond (SER195 and GLN192), hydrophobic (GLN192 and HIS57) and π-π stacking bonding (HIS57). The stability of trypsin@C440 bio-conjugate at higher temperature was established from temperature dependent PL studies and the thermodynamic parameters determined agree with second law of thermodynamics. The thermodynamic parameters such as change in enthalpy (ΔH=172.2Jmol−1), change in entropy (ΔS=15.3Jmol−1K−1) and the respective approximately same and unity values of Gibb's free energy (ΔG) and Hill coefficient (n), as well as binding affinities determined from temperature dependent fluorescence studies validate the hydrophobic, spontaneous, exothermic process engaged in trypsin@C440 bio-conjugate.