Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA.
Departments of Biological Sciences and Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, IN 47907, USA.
Biomolecules. 2021 Mar 17;11(3):447. doi: 10.3390/biom11030447.
G protein-coupled receptors (GPCRs), which regulate a vast number of eukaryotic processes, are desensitized by various mechanisms but, most importantly, by the GPCR kinases (GRKs). Ever since GRKs were first identified, investigators have sought to determine which structural features of GRKs are used to select for the agonist-bound states of GPCRs and how this binding event in turn enhances GRK catalytic activity. Despite a wealth of molecular information from high-resolution crystal structures of GRKs, the mechanisms driving activation have remained elusive, in part because the GRK N-terminus and active site tether region, previously proposed to serve as a receptor docking site and to be key to kinase domain closure, are often disordered or adopt inconsistent conformations. However, two recent studies have implicated other regions of GRKs as being involved in direct interactions with active GPCRs. Atomic resolution structures of GPCR-GRK complexes would help refine these models but are, so far, lacking. Here, we assess three distinct models for how GRKs recognize activated GPCRs, discuss limitations in the approaches used to generate them, and then experimentally test a hypothetical GPCR interaction site in GRK2 suggested by the two newest models.
G 蛋白偶联受体 (GPCRs) 调控着大量真核生物过程，通过多种机制失敏，但最重要的是通过 G 蛋白偶联受体激酶 (GRKs)。自从首次鉴定出 GRKs 以来，研究人员一直在试图确定 GRKs 的哪些结构特征被用于选择激动剂结合的 GPCR 状态，以及这种结合事件如何反过来增强 GRK 的催化活性。尽管从 GRKs 的高分辨率晶体结构中获得了丰富的分子信息，但激活的机制仍然难以捉摸，部分原因是 GRK 的 N 端和活性位点连接区，先前被提议作为受体 docking 位点，并且是激酶结构域关闭的关键，通常是无序的或采用不一致的构象。然而，最近的两项研究表明，GRKs 的其他区域可能参与与活性 GPCR 的直接相互作用。GPCR-GRK 复合物的原子分辨率结构将有助于完善这些模型，但目前仍缺乏这些结构。在这里，我们评估了 GRKs 识别激活的 GPCR 的三种不同模型，讨论了生成这些模型的方法的局限性，然后通过实验测试了由最新的两个模型提出的 GRK2 中的一个假设的 GPCR 相互作用位点。
