Interactions of tetracyclines with milk allergenic protein (casein): a molecular and biological approach

Abstract

Tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC) interactions with the allergenic milk protein casein (CAS) were here evaluated simulating food conditions. The antibiotics assessed interact with CAS through static quenching and form non-fluorescent complexes. At 30 °C, the binding constant (K_b) varied from 0.05 to 1.23 × 10⁶ M⁻¹. Tetracycline interacts with CAS preferably through electrostatic forces, while oxytetracycline and chlortetracycline interactions occur by hydrogen bonds and van der Waals forces. The interaction process is spontaneous, and the magnitude of interaction based on K_b values, followed the order: TC < CTC < OTC. The distances between the donor (protein) and the receptors (TC, OTC, and CTC) were determined by Förster resonance energy transfer (FRET) and varied from 3.67 to 4.08 nm. Under natural feeding conditions, the citrate decreased the affinity between TC and CAS; a similar effect was observed for OTC in the presence of Ca(II), Fe(III) and lactose. Synchronized and three-dimensional (3D) fluorescence studies indicated alterations in the original protein conformation due to the interaction process, which may influence allergenic processes. In addition, complexation with CAS modulated the antimicrobial activity of CTC against S. aureus, demonstrated that the interaction process possibly alters the biological properties of antibiotics and the own protein, in the food conditions.

Communicated by Ramaswamy H. Sarma

Graphical Abstract

Keywords:

• Milk proteins
• antibiotics and allergenicity
• antibacterial activity

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

We thank the Universidade Federal de Alagoas (UFAL), Instituto de Química e Biotecnologia (IQB), Programa de Pós-graduação em Química e Biotecnoligia (PPGQB) by infrastructure, and FAPEAL (Process number 60030 000863/2016), Fundação de Apoio ao Desenvolvimento do Ensino, Ciência e Tecnologia do Estado de Mato Grosso do Sul (FUNDECT), Fundação de Apoio a Pesquisa do Distrito Federal (FAPDF) for financial support. In addition, this study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001, and CNPq for financial support and fellowships.