STRUCTURAL STUDIES OF FOLLISTATIN ISOFORMS BY SAXS IN SOLUTION

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 卵泡抑素剪接变异体FS288和FS315表现出独特的功能和生理特性，例如在转化生长因子-b配体和硫酸肝素结合以及血清和组织定位方面的差异。在FS288C末端增加28个氨基酸可能会通过改变蛋白质的构象来影响卵泡抑素的功能，从而降低其与两个已知配体的亲和力。基于我们对FS315：激活素A晶体结构的分析，我们假设FSD3可能与FS315的C末端结合，并将其呈现给与FSD1肝素结合位点重叠的内部相互作用位点。这个模型将解释FS亚型之间的功能差异，并且应该可以使用生物物理方法进行测试。为了影响FS的配基结合亲和力，FS315的C末端可能会导致游离FS结构的显著构象变化，如紧凑或约束多肽链的结构。预计尾巴与HBS的相互作用将显著改变单体蛋白质的形状，潜在地减小分子的整体直径，并产生更球形的结构域排列。我们建议使用小角X射线散射来测试蛋白质在溶液中的这种可能性。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Follistatin splice variants, FS288 and FS315, exhibit unique functional and physiological characteristics, such as differences in TGF-b ligand and heparan sulfate binding and serum vs. tissue localization. The addition of 28 amino acids to the FS288 C-terminus may influence follistatin functions by altering the conformation of the protein, thereby decreasing its affinity for both of its known ligands. Based on our analysis of the FS315:activin A crystal structure, we hypothesize that FSD3 may bind to and present the FS315 C-terminal tail to an internal interaction site that overlaps the FSD1 heparin binding site. This model would explain the functional differences between FS isoforms and should be testable using biophysical approaches. In order to influence the ligand binding affinity of FS, the FS315 C-terminus likely induces significant conformational changes in the free FS structure, such as compacting or constraining the structure of the polypeptide chain. The interaction of the tail with the HBS would be predicted to significantly change the shape of the monomeric protein, potentially reducing the overall diameter of the molecule and producing a more globular arrangement of the domains. We propose to test this possibility for the protein in solution using small angle x-ray scattering.