The increasing problem of multidrug resistance (MDR) in bacteria calls for discovery of new molecules and diagnostic methodologies that are effective against a wide range of microbial pathogens. We have studied the role of alexidine dihydrochloride (alex) as a bioaffinity ligand against lipopolysaccharide (LPS), a pathogen-associated surface marker universally present on all Gram-negative bacteria. While the activity of alex against bacteria is biologically known, little information exists on its mechanism of action or binding stoichiometry. We have used nuclear magnetic resonance (NMR), fluorescence, and surface plasmon resonance (SPR) spectroscopies to probe the binding characteristics of alex and LPS molecules. Our results indicate that LPS:alex stoichiometry lies between 1:2 and 1:4 and has a dissociation constant (K_D) of 38 μM that is mediated through electrostatic interactions between the negatively charged phosphate groups present on LPS and the positively charged guanidinium groups present in alex. Further, molecular dynamics (MD) simulations performed to determine the conformational interaction between the two molecules show good agreement with the experimental results, which substantiate the potential of alex molecule for LPS neutralization and hence, development of efficient in vitro diagnostic assays.

中文翻译：

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光谱法和计算机模拟方法对脂多糖与亚乙基吡啶相互作用的机理进行评估

细菌中多重耐药性（MDR）日益严重的问题要求发现对许多微生物病原体有效的新分子和诊断方法。我们已经研究了盐酸阿里西啶二盐（alex）作为针对脂多糖（LPS）的生物亲和配体的作用，脂多糖是普遍存在于所有革兰氏阴性细菌上的病原体相关表面标记。虽然alex对细菌的活性是生物学已知的，但关于其作用机理或结合化学计量的信息很少。我们已经使用核磁共振（NMR），荧光和表面等离振子共振（SPR）光谱来探测alex和LPS分子的结合特征。我们的结果表明LPS：alex的化学计量比介于1：2和1：4之间，并且具有解离常数（K_D）为38μM，这是通过LPS上带负电荷的磷酸基团和alex上带正电荷的胍基团之间的静电相互作用介导的。此外，执行分子动力学（MD）模拟以确定两个分子之间的构象相互作用显示出与实验结果良好的一致性，这证实了亚历克斯分子对LPS中和的潜力，因此，开发了有效的体外诊断测定方法。