Biophysical and molecular modeling evidences for the binding of sulfa molecules with hemoglobin

The molecular mechanism of the heme protein, hemoglobin (Hb) interaction with sulfa molecule, sulfadiazine (SDZ) has been investigated through spectroscopic, neutron scattering and molecular modeling techniques. Absorption and emission spectroscopic studies showed that SDZ molecules were bound to Hb protein, non-cooperatively. The binding affinityof SDZ-Hb complex at standard experimental condition was evaluated to be around (4.2 ± 0.07) ×10⁴, M⁻¹with 1:1 stoichiometry. Drug induced structural perturbation of the 3 D protein moiety was confirmed through circular dichroism (CD), synchronous fluorescence and small angle neutron scattering methods. From the temperature dependent spectrofluorometric studies, the negative standard molar Gibbs energy change suggested the spontaneity of the reaction. The negative enthalpy and positive entropy change(s) indicated towards the involvement of both electrostatic and hydrophobic forces during the association process. Salt dependent fluorescence study revealed major contributions from non-poly-electrolytic forces. Molecular modeling studies determined the probable binding sites, types of interaction involved and the conformational alteration of the compactness of the Hb structure upon interaction with SDZ molecule. Overall, the study provides detailed insights into the binding mechanism of SDZ antibiotics to Hb protein. Communicated by Ramaswamy H. Sarma

本研究采用光谱学、中子散射及分子建模技术，对血红素蛋白血红蛋白（hemoglobin, Hb）与磺胺类分子磺胺嘧啶（sulfadiazine, SDZ）的相互作用分子机制进行了探究。吸收与发射光谱学研究显示，SDZ分子以非协同方式与Hb蛋白结合。在标准实验条件下，SDZ-Hb复合物的结合亲和力经测定约为(4.2 ± 0.07)×10⁴ M⁻¹，结合计量比为1:1。通过圆二色光谱（circular dichroism, CD）、同步荧光及小角中子散射技术，证实了药物诱导的Hb蛋白三维结构发生扰动。基于温度依赖性荧光光谱研究，负向标准摩尔吉布斯自由能变表明该结合反应具有自发性；负焓变与正熵变则提示，二者结合过程中同时存在静电作用力与疏水作用力。盐依赖性荧光实验显示，非聚电解质作用力是相互作用的主要贡献来源。分子建模研究明确了SDZ与Hb相互作用的潜在结合位点、参与的相互作用类型，以及Hb结构紧凑性发生的构象变化。总体而言，本研究详细阐明了SDZ类抗生素与Hb蛋白的结合机制。本稿件由Ramaswamy H. Sarma通讯