TERTIARY STRUCTURES OF ACTIVIN AND ACTIVIN RECEPTORS

这项研究的目的是了解生物信号是如何通过各种靶细胞的膜进行转导的。神经内分泌肽、激活素具有广泛的生物学功能，为研究其作用机制提供了良好的系统。涉及两种类型的受体，以在它们与激活素配体顺序结合时触发信号级联。这些跨膜蛋白各自具有单个跨膜螺旋和细胞质Ser/Thr激酶结构域。我们的目标是有一个结构上的理解如何结合的激活素的第一个受体（II型激活素受体，ActRII）的胞外结构域，然后被转导到下游组件的信号传导途径，以激活激酶活性的I型受体（ActRII），这与激活素/ActRII复合物。我们的主要重点是确定ActRII（ActRII-ECD）与激活素配体或ActRII-ECD或两者复合的胞外配体结合结构域的结构。我们目前已经获得了与激活素配体复合的ActRII-ECD的单晶。我们还建立了ActRII-ECD的高水平表达以获得单晶。基于不同配体/受体复合物的化学计量比和结合亲和力，其中异源二聚体（不对称）或同源二聚体（对称）配体，如阿替宾或激活素，分别与两种不同类型的受体（不对称）的寡聚体复合物相互作用，我们将建立该过程的热力学和动力学速率。扩展我们以前的工作，1.5 A晶体结构的行为RII-ECD单独，我们希望提供一个结构基础，相关的配体和受体成分之间的复合物形成后诱导的构象变化的跨膜信号传导机制。激活素的重组形式、激活素拮抗剂、ActRII-ECD现在可以大量获得，以进行各种复合物的化学表征和晶体结构测定。结果将提供一个坚实的基础，以表征这种无处不在的神经肽的结合特异性，从中我们可以促进有效的和持久的拟肽药物的设计，用于调制各种疾病相关的疾病和人口控制。

The goal of the proposed study is to understand how biological signal is transduced across the membrane of a variety of target cells. Neuroendocrine peptides, activins exert a wide range of biological functions, which provides an excellent system to study such mechanisms. Two types of receptors are involved to trigger the signaling cascade upon their sequential binding to activin ligand. These are transmembrane proteins each with a single transmembrane helix and a cytoplasmic Ser/Thr kinase domain. Our goal is to have a structural understanding of how the binding of activin to the extracellular domain of the first receptor (type II activin receptor, ActRII) is then transduced to the downstream components of the signaling pathway to activate the kinase activity of the type I receptor (ActRII), which complexes with activin/ActRII complex. Our primary focus is on the structure determination of the extracellular, ligand-binding domain of ActRII (ActRII-ECD) in complex with either activin ligand, or ActRII-ECD, or both. We have currently obtained single crystals of ActRII-ECD in complex with activin ligand. We have also established high-level expression of ActRII-ECD to obtain single crystals. Based on stoichiometric ratios and binding affinity of different ligand/receptor complexes, in which either a heterodimeric (asymmetric) or homodimeric (symmetric) ligands, such as inhibin or activin, respectively, interacts with oligomeric complexes of two different types of receptor (asymmetric), we will establish the thermodynamic and kinetic rates of the processes. Expanding on our previous work on 1.5 A crystal structure of Act RII-ECD alone, we hope to provide a structural basis to correlate conformational changes induced upon complex formation between the ligand and receptor components to the transmembrane signaling mechanism. Recombinant forms of activins, inhibins (activin antagonist), ActRII-ECD are now available in large enough quantities to carry out chemical characterization and crystal structure determination of various complexes. Results will provide a firm basis to characterize the binding specificity of this ubiquitous neuropeptide, from which we can facilitate the design of effective and long-lasting peptidomimetic drugs to be used in modulating various hormone-related diseases and in population control.