Antenna effect and phosphorescence spectra to find the location of drug tetracycline in bovine β-lactoglobulin A
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A ternary system comprising of a Eu(III) complex of the drug Tetracycline hydrochloride (Eu3TC) bound to bovine β-lactoglobulin variant A (BLGA) in aqueous buffer at physiological pH (pH = 7.4) has been investigated to exploit the enhanced “antenna effect” to locate the bound drug and find the microenvironment of the binding site. Steady-state and time-resolved emission studies at room temperature as well as at 77 K have been carried out to evaluate the binding parameters in the binary system consisting of BLGA and tetracycline hydrochloride (TC). Low-temperature phosphorescence studies at 77 K of pure BLGA confirm Trp 19 to be the emitting residue, while Trp 61 is silent. Enhancement of BLGA phosphorescence emission in the ternary system at 77 K indicates that Trp 19 is very close to Eu(III) in the Eu3TC complex. The molecular docking results further confirm that TC binds close to Trp 19 in a hydrophobic domain. The results thus obtained can provide guidelines to design and synthesize target-oriented drugs as well as suitable bio-probes.
KeywordsAntenna effect Bovine β-lactoglobulin Tetracycline Fluorescence Phosphorescence Accessible surface area
S. G. gratefully acknowledges the Department of Science and Technology (DST), Government of India (Grant no.: SB/S1/PC-003/2013), and MBR gratefully acknowledges UGC [Minor Research Project No.F.PS-146/15-16 (ERO)] for financially supporting this work.
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