The interaction of beta-lactoglobulin with ciprofloxacin and kanamycin; a spectroscopic and molecular modeling approach

A vast research has been conducted to find suitable and safe carriers for vital and pH-sensitive drugs including antibiotics. This article reports the use of easily accessible and abundant purified beta-lactoglobulin (β-LG) protein as the potential carrier of widely used Kanamycin (<b>Kana</b>) and Ciprofloxacin (<b>Cip</b>) antibiotics. Spectroscopic techniques (Fluorescence, UV–vis, Circular Dichroism) combined with molecular docking were used to determine the binding mechanism of these drugs. Fluorescence studies showed moderate binding affinity with the calculated binding constants <i>K</i>_Cip = 60.1 (±0.2) × 10³ M⁻¹ and <i>K</i>_kana = 2.5 (±0.6) × 10³ M⁻¹ with the order of <b>Cip</b> &gt; <b>Kana</b>. Results of UV–vis were consistent with fluorescence measurements and demonstrated a stronger complexation for <b>Cip</b> rather than <b>Kana</b>. The secondary structure of β-LG was preserved upon interaction with <b>Kana</b>; however, a reduction in β-sheet content from 39.1 to 31.9% was convoyed with an increase in α-helix from 12.8 to 20.5% due to complexation of <b>Cip</b>. Molecular docking studies demonstrated that preferred binding sites of these drugs are not the same and several amino acids are involved in stabilizing the interaction. Based on the achieved results, <b>Kana</b> and <b>Cip</b> can spontaneously bind to β-LG and this protein may serve as their transport vehicle.

学界已开展大量研究，旨在开发适用于包括抗生素在内的关键pH敏感型药物的安全递送载体。本文报道了利用易得且储量丰富的纯化β-乳球蛋白（beta-lactoglobulin, β-LG）作为常用抗生素卡那霉素（Kanamycin, Kana）与环丙沙星（Ciprofloxacin, Cip）的潜在递送载体。
本研究结合光谱技术（荧光光谱、紫外-可见光谱、圆二色谱）与分子对接法，解析了两种药物与载体的结合机制。荧光光谱分析结果显示二者均具有中等结合亲和力，计算得到的结合常数分别为K_Cip = 60.1(±0.2)×10³ M⁻¹、K_kana = 2.5(±0.6)×10³ M⁻¹，结合亲和力排序为Cip > Kana。
紫外-可见光谱实验结果与荧光光谱分析结果一致，同样表明环丙沙星与β-LG的络合作用强于卡那霉素。卡那霉素与β-LG结合后，其二级结构得以保留；而环丙沙星与β-LG络合后，β-折叠含量从39.1%降至31.9%，同时α-螺旋含量从12.8%提升至20.5%。
分子对接实验结果显示，两种药物与β-LG的优选结合位点存在差异，且均有多个氨基酸残基参与稳定二者的相互作用。综上实验结果，卡那霉素与环丙沙星均可与β-LG自发结合，该蛋白可作为二者的药物递送载体。