Molecular Dynamics Simulations Reveal Fundamental Role of Water As Factor Determining Affinity of Binding of β-Blocker Nebivolol to β₂-Adrenergic Receptor

The β-adrenergic antagonists (β-blockers) constitute a class of drugs that have well-established roles in treatments of various cardiovascular diseases. Despite a 50 year history, there are two clinically important subtypes of β-adrenergic receptors (βARs) called β1AR and β2AR that still are promising drug targets. Our study maps the interactions between nebivolol―one of the most efficient β-blocking agents―and the β2-adrenergic receptor by simulating two optical isomers of nebivolol: ssss-nebivolol and srrr-nebivolol. The srrr-configuration binds preferentially to β1AR and β2AR. The ssss-form has much lower binding affinity to both of them. Our work indicates that water is a very important component of the binding site of the β2AR receptor. We found that the higher stereoselectivity of the srrr-configuration is due to interactions with water molecules, which extensively hydrate the binding site of β2AR. By lowering the energy of binding, water enhanced the affinity of the srrr-form to β2AR. We also address the problem of β1AR/β2AR selectivity. At higher concentrations, all β-blocking agents lose their specificity and bind nonselectively, causing many adverse effects. Our simulations indicate that PHE194, TYR308, and ILE309 of the β2AR and the corresponding residues of the β1AR receptor may be important determinants of β1AR versus β2AR selectivity.β肾上腺素能拮抗剂（β-adrenergic antagonists，β-blockers）是一类经临床证实可有效治疗多种心血管疾病的药物。尽管此类药物已有50年的应用历史，但两类具有重要临床价值的β肾上腺素能受体（β-adrenergic receptors, βARs）亚型——β1AR与β2AR，仍是极具潜力的药物作用靶点。本研究针对奈必洛尔（nebivolol）——目前最有效的β受体阻滞剂之一——的两种光学异构体：ssss-奈必洛尔与srrr-奈必洛尔，通过模拟手段阐明了其与β2肾上腺素能受体的相互作用机制。其中，srrr构型对β1AR和β2AR均具有优先结合能力，而ssss构型对二者的结合亲和力则显著更低。本研究结果表明，水分子是β2AR结合位点的关键组成部分。我们发现，srrr构型所展现出的更高立体选择性，源于其与水分子的相互作用：β2AR的结合位点被水分子广泛水合，水分子通过降低结合自由能，增强了srrr构型与β2AR的结合亲和力。此外，本研究还探讨了β1AR/β2AR的选择性问题。当药物浓度升高时，所有β受体阻滞剂都会丧失特异性，产生非选择性结合并引发多种不良反应。我们的模拟结果显示，β2AR的PHE194、TYR308、ILE309残基，以及β1AR的对应残基，可能是决定β1AR与β2AR选择性的关键因素。