Follistatin-Molecular Structure/Function

描述（由申请人提供）：该项目的目标是确定结构域结构的作用并确定卵泡抑素生物活性的结构要求，卵泡抑素是一种多结构域蛋白，可结合垂体、骨骼和多种其他组织和生理系统中的激活素并对其进行生物中和。迄今为止，我们对 288 个残基的卵泡抑素分子的研究集中于化学修饰和诱变对激活素结合的功能影响，以及与促进卵泡抑素组织定位的细胞表面硫酸乙酰肝素蛋白聚糖的关联。这些结果表明，63 个残基的 N 端结构域加上三个独特的 10-半胱氨酸“卵泡抑素”(FS) 结构域中的前两个结构域是激活素结合所必需的，并且疏水性残基对于激活素相互作用和结构域构象的维持都特别重要。在这次更新中，我们将使用晶体学和突变分析的互补方法来检查域间关系和激活素结合成分的组织，以提供卵泡抑素分子的功能模型。在目标 1 下，我们将通过结晶和 X 射线衍射分析确定纯化的 follistatin-288 分子的 3 维结构。将在全长卵泡抑素和（如果需要提高分辨率）双结构域片段上进行结构，从无血清培养基中的 293F 细胞悬浮培养物中纯化。在目标 2 中，我们将制备与激活素复合的卵泡抑素，用于晶体学分析，以直接识别接触位点并记录复合物形成过程中关键决定因素所经历的变化。 Aim 3 下的激活素配体的突变分析将补充并在功能上验证激活素-卵泡抑素复合物的晶体分析所开发的结构。功能上重要的疏水表面残基的鉴定将检验我们的假设，即卵泡抑素通过与激活素受体中已知的疏水位点竞争而发挥作用。这些研究将阐明广泛假设的卵泡抑素局部调节激活素的机制，增强对 TGF-β 家族其他有效结合蛋白（如头蛋白和脊索蛋白）特征活性的理解，并扩大我们对卵泡抑素结构域结构在许多其他胞外蛋白中的一般作用的认识。

DESCRIPTION (provided by applicant): The goal of this project has been to establish the role of domain structure and determine the structural requirements for the biological activity of follistatin, a multidomain protein that binds and bioneutralizes activin in pituitary, bone and a wide range of other tissues and physiological systems. Our investigations to date of the 288-residue follistatin molecule have concentrated on functional effects of chemical modifications and mutagenesis on activin binding, as well as on association with cell-surface heparan-sulfate proteoglycans that promote follistatin's tissue localization. These have shown that the 63-residue N-terminal domain plus the first two of the three distinctive 10-cysteine "follistatin" (FS) domains are required for activin binding, and that hydrophobic residues are particularly important both to activin interaction and maintenance of domain conformation. Under this renewal, we will use complementary approaches of crystallography and mutational analysis to examine interdomain relationships and the organization of activin-binding components to provide a functional model of the follistatin molecule. Under Aim 1 we will determine the 3-dimensional structure of the purified follistatin-288 molecule by crystallization and x-ray diffraction analysis. Structures will be done on full-length follistatin and (if needed to enhance resolution) two-domain segments, purified from 293F-cell suspension cultures in serum-free medium. In Aim 2 we will prepare follistatin complexed with activin for crystallography to directly identify contact sites and document changes undergone by key determinants during complex formation. Mutational analyses of the activin ligand under Aim 3 will complement and functionally validate the structures developed from crystallographic analysis of the activin-follistatin complex. Identification of functionally important hydrophobic surface residues will test our hypothesis that follistatin acts through competition with known hydrophobic sites in the activin receptor. These investigations will clarify the mechanism of the widely-postulated local regulation of activin by follistatin, enhance understanding of the activity of other potent binding proteins (such as noggin and chordin) characteristic of the TGF-beta family and expand our insight into the role of follistatin-domain structures in general among the many other extracellular proteins in which they can be found.