小柯机器人

英国MRC分子生物学实验室Christopher G. Tate及其研究小组阐明了β-arrestin（βarr1）与福莫特罗结合β1-肾上腺素受体（β1AR）的分子基础。 相关论文于2020年6月17日在线发表在《自然》杂志上。

为了解抑制蛋白偶联的分子基础，研究人员解析了与偏好性激动剂福莫特罗结合的脂质纳米盘中β1AR–βarr1复合物的冷冻电镜结构，以及福莫特罗结合的β1AR与G蛋白模拟纳米抗体Nb80的晶体结构。βarr1以与Gs耦合至β2AR Gs7不同的方式耦合至β1AR，βarr1的指环在细胞内表面上的裂隙较窄，并且与Gs C端的α5螺旋相比更靠近受体的跨膜螺旋H7。βarr1中指环的构象与视紫红质抑制蛋白中指环与视紫红质偶联时所采用的构象不同。和Nb80偶联的β1AR相比，与βarr1偶联的β1AR在结构上存在显著差异，包括细胞外环3的向内运动以及H5和H6的胞质末端。

研究人员观察到福莫特罗与β1AR正构结合位点H5中两个丝氨酸残基之间的相互作用减弱，福莫特罗对β1AR-βarr1复合物的亲和力比对β1AR-Gs复合物的亲和力低。β1AR的这些复合物之间的结构差异为设计可能偏向β-肾上腺素受体信号传导的小分子提供了基础。

研究人员表示，β1AR是与异三聚体G蛋白Gs偶联的G蛋白偶联受体（GPCR）。GPCR激酶（GRKs）受体C末端的磷酸化与β-arrestin1（也称为抑制蛋白）偶联可终止G蛋白介导的信号传导，从而取代Gs并通过MAP诱导信号传导激酶途径。合成激动剂优先通过G蛋白或抑制蛋白诱导信号转导的能力（又称偏好性激动剂）而在药物开发中很重要，因为治疗效果可能仅来自一个信号级联反应，而另一种途径可能介导不良副作用。

附：英文原文

Title: Molecular basis of β-arrestin coupling to formoterol-bound β 1 -adrenoceptor

Author: Yang Lee, Tony Warne, Rony Nehm, Shubhi Pandey, Hemlata Dwivedi-Agnihotri, Madhu Chaturvedi, Patricia C. Edwards, Javier Garca-Nafra, Andrew G. W. Leslie, Arun K. Shukla, Christopher G. Tate

Issue&Volume: 2020-06-17

Abstract: The β1-adrenoceptor (β1AR) is a G-protein-coupled receptor (GPCR) that couples1 to the heterotrimeric G protein Gs. G-protein-mediated signalling is terminated by phosphorylation of the C terminus of the receptor by GPCR kinases (GRKs) and by coupling of β-arrestin 1 (βarr1, also known as arrestin 2), which displaces Gs and induces signalling through the MAP kinase pathway2. The ability of synthetic agonists to induce signalling preferentially through either G proteins or arrestins—known as biased agonism3—is important in drug development, because the therapeutic effect may arise from only one signalling cascade, whereas the other pathway may mediate undesirable side effects4. To understand the molecular basis for arrestin coupling, here we determined the cryo-electron microscopy structure of the β1AR–βarr1 complex in lipid nanodiscs bound to the biased agonist formoterol5, and the crystal structure of formoterol-bound β1AR coupled to the G-protein-mimetic nanobody6 Nb80. βarr1 couples to β1AR in a manner distinct to that7 of Gs coupling to β2AR—the finger loop of βarr1 occupies a narrower cleft on the intracellular surface, and is closer to transmembrane helix H7 of the receptor when compared with the C-terminal α5 helix of Gs. The conformation of the finger loop in βarr1 is different from that adopted by the finger loop of visual arrestin when it couples to rhodopsin8. β1AR coupled to βarr1 shows considerable differences in structure compared with β1AR coupled to Nb80, including an inward movement of extracellular loop 3 and the cytoplasmic ends of H5 and H6. We observe weakened interactions between formoterol and two serine residues in H5 at the orthosteric binding site of β1AR, and find that formoterol has a lower affinity for the β1AR–βarr1 complex than for the β1AR–Gs complex. The structural differences between these complexes of β1AR provide a foundation for the design of small molecules that could bias signalling in the β-adrenoceptors.

DOI: 10.1038/s41586-020-2419-1

Source: https://www.nature.com/articles/s41586-020-2419-1

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