Department of Biological Sciences, Indian Institute of Science Education and Research Bhopal, Bhopal Bypass Road, Bhopal 462066, MP, India.
Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhopal Bypass Road, Bhopal 462066, MP, India.
J Phys Chem B. 2022 Mar 10;126(9):1917-1932. doi: 10.1021/acs.jpcb.1c08610. Epub 2022 Feb 23.
The large conformational flexibility of G protein-coupled receptors (GPCRs) has been a puzzle in structural and pharmacological studies for the past few decades. Apart from structural rearrangements induced by ligands, enzymatic phosphorylations by GPCR kinases (GRKs) at the carboxy-terminal tail (C-tail) of a GPCR also make conformational alterations to the transmembrane helices and facilitates the binding of one of its transducer proteins named β-arrestin. The phosphorylation-induced conformational transition of the receptor that causes specific binding to β-arrestin but prevents the association of other transducers such as G proteins lacks atomistic understanding and is elusive to experimental studies. Using microseconds of all-atom conventional and Gaussian accelerated molecular dynamics (GaMD) simulations, we investigate the allosteric mechanism of phosphorylation induced-conformational changes in β-adrenergic receptor, a well-characterized GPCR model system. Free energy profiles reveal that the phosphorylated receptor samples a new conformational state in addition to the canonical active state corroborating with recent nuclear magnetic resonance experimental findings. The new state has a smaller intracellular cavity that is likely to accommodate β-arrestin better than G protein. Using contact map and inter-residue interaction energy calculations, we found the phosphorylated C-tail adheres to the cytosolic surface of the transmembrane domain of the receptor. Transfer entropy calculations show that the C-tail residues drive the correlated motions of TM residues, and the allosteric signal is relayed via several residues at the cytosolic surface. Our results also illustrate how the redistribution of inter-residue nonbonding interaction couples with the allosteric communication from the phosphorylated C-tail to the transmembrane. Atomistic insight into phosphorylation-induced β-arrestin specific conformation is therapeutically important to design drugs with higher efficacy and fewer side effects. Our results, therefore, open novel opportunities to fine-tune β-arrestin bias in GPCR signaling.
G 蛋白偶联受体（GPCR）的构象灵活性在过去几十年的结构和药理学研究中一直是一个难题。除了配体诱导的结构重排外，GPCR 羧基末端尾巴（C 尾）上的 GPCR 激酶（GRK）的酶促磷酸化也会使跨膜螺旋发生构象改变，并促进一种名为β-arrestin 的转导蛋白的结合。这种受体的磷酸化诱导的构象转变导致与β-arrestin 的特异性结合，但阻止了其他转导蛋白（如 G 蛋白）的结合，其原子水平的理解缺乏，实验研究也难以捉摸。使用微秒的全原子常规和高斯加速分子动力学（GaMD）模拟，我们研究了β-肾上腺素能受体的磷酸化诱导构象变化的变构机制，β-肾上腺素能受体是一种经过充分研究的 GPCR 模型系统。自由能曲线揭示，除了经典的活性状态外，磷酸化受体还可以采样到一种新的构象状态，这与最近的核磁共振实验结果相符。新状态具有更小的细胞内腔，可能比 G 蛋白更好地容纳β-arrestin。使用接触图和残基间相互作用能计算，我们发现磷酸化的 C 尾附着在受体跨膜域的胞质表面。转移熵计算表明，C 尾残基驱动 TM 残基的相关运动，变构信号通过胞质表面的几个残基传递。我们的结果还说明了残基间非键相互作用的重新分布如何与来自磷酸化 C 尾的变构通讯相耦合，传递到跨膜。对磷酸化诱导的β-arrestin 特异性构象的原子水平的了解对于设计具有更高疗效和更少副作用的药物具有重要的治疗意义。因此，我们的结果为精细调整 GPCR 信号转导中的β-arrestin 偏向提供了新的机会。
