Abstract
Bovine casein was used as a model protein to explore the binding behavior of food matrix with residual antibiotics. The interaction mechanism between casein and tetracycline (TC) was characterized by fluorescence quenching and isothermal titration calorimetry. Through forming the non-fluorescent ground-state complex, TC effectively quenched the endogenous fluorescence of casein. The formed casein-TC complex was maintained by hydrogen bonding, electrostatic and hydrophobic interactions (ΔH < 0, ΔS > 0). Circular dichroism and infrared spectroscopic studies indicated that the complexation of TC did not affect the secondary structure of casein. Molecular docking further theoretically validated the main interaction forces and deciphered the amino acid residues surrounding the antibiotic in the casein binding pocket. Interestingly, 1H NMR results demonstrated the π-π stacking interaction formed between PHE-189 and the benzene ring of TC, which was consistent with the docking findings. Besides, saturation transfer difference (STD) NMR revealed that the binding of TC engages its –N(CH3)2 group. This study sheds new light on the transition of residual antibiotics from the free to the bound state in foodstuffs.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have