STRUCTURAL STUDIES OF FOLLISTATIN ISOFORMS BY SAXS IN SOLUTION

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目及 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 卵泡抑素剪接变体FS 288和FS 315表现出独特的功能和生理特征，例如TGF-β配体和硫酸乙酰肝素结合以及血清与组织定位的差异。 在FS 288 C-末端添加28个氨基酸可能通过改变蛋白质的构象来影响卵泡抑素功能，从而降低其对两种已知配体的亲和力。 基于我们对FS 315：激活素A晶体结构的分析，我们假设FSD 3可能与FSD 1肝素结合位点重叠的内部相互作用位点结合并将FS 315 C末端尾呈递给该位点。 该模型将解释FS异构体之间的功能差异，并应使用生物物理方法进行测试。为了影响FS的配体结合亲和力，FS 315 C-末端可能诱导游离FS结构中的显著构象变化，例如压缩或约束多肽链的结构。 尾部与HBS的相互作用将被预测为显著改变单体蛋白的形状，潜在地减小分子的总直径并产生结构域的更球形的排列。 我们建议使用小角X射线散射测试这种可能性的蛋白质溶液。

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.