Ligand-receptor interactions in the TGF-beta superfamily

描述（由申请人提供）：TGF β和TGF β超家族的其他结构相关蛋白，如BMP，GDF和激活素，是分泌的信号蛋白，调节许多基本过程，从胚胎发育期间的身体计划的建立到适应性免疫系统的调节。超过30个超家族成员的重要性被许多由该途径失调引起的人类疾病所证明，包括骨骼和心脏疾病、不孕症和癌症。开发用于治疗途径相关疾病的有效疗法需要了解支配配体活性的相互作用-这包括与信号传导受体的相互作用，以及与结合配体并调节配体可及性的许多辅助蛋白的相互作用。这个项目的目标是利用我们目前的理解 TGF β如何结合其信号受体，以研究betaglycan，一种膜锚定的辅助结合蛋白聚糖，一方面促进TGF β信号传导，另一方面抑制激活素信号传导。β聚糖增强TGF β信号传导被认为是由于其结合和定位细胞表面TGF β配体的能力。为了研究这一点，我们将确定β聚糖的两个独立的TGF β结合域的结构，BGE和BGU，结合到TGF β使用晶体学，这是理想的这些目的，因为BGE和BGU结合并形成高度稳定的复合物与TGF β。将在功能测定中测试由复合物的结构所提示的受体结合的增强机制。β聚糖对激活素信号传导的抑制被认为是通过激活素II型受体ActRII或其同源物ActRIIb与β聚糖和β聚糖A形成三元复合物来介导的，β聚糖A是一种异源二聚体配体，具有结合激活素II型受体ActRII/ActRIIb的激活素β亚基和激活素β亚基。 结合BGU，β聚糖的C-末端结合域。为了研究这一点，我们将首先确定激活素如何结合其I型受体ActRIb。这些研究将使用NMR进行，因为ActRIb与激活素A的结合较弱。这将通过使用晶体学确定与BGU结合的BGU bin A的结构来进一步研究，这对于这些目的是理想的，因为BGU与BGU bin A结合并形成高度稳定的复合物。将在功能测定中测试由复合物的结构所建议的由阿替宾A拮抗激活素的机制。所提出的研究的可行性是通过衍射获得的BGE：T-RII：TGF-β复合物的晶体，分离BGUC：TGF-β复合物的能力，以及ActRIb的NMR信号分配来证明的。这些结构的确定将为我们理解超家族的辅助蛋白之一β聚糖如何影响TGF β和激活素诱导的下游信号传导提供一个重要的缺失环节。这些结构还将有助于开发新的靶向疗法，用于治疗由异常TGF β和激活素信号传导引起的疾病和病症，如癌症和不育症。

DESCRIPTION (provided by applicant): TGF�s and other structurally related proteins of the TGF� superfamily, such as BMPs, GDFs, and activins, are secreted signaling proteins that regulate many essential processes, ranging from establishment of the body plan during embryogenesis to regulation of the adaptive immune system. The importance of the more than 30 superfamily members is demonstrated by the many human diseases that result from dysregulation of the pathway, including skeletal and cardiac disorders, infertility, and cancer. The development of effective therapies for treating pathway-associated diseases requires knowledge of the interactions that govern ligand activities - this includes interactions with the signaling receptors, but as well with the many accessory proteins that bind ligands and regulate ligand accessibility. The objective of this project is to capitalize upon our current understanding of how TGF�s bind their signaling receptors to investigate how betaglycan, a membrane-anchored accessory binding proteolgycan, functions on the one hand to promote TGF� signaling, and on the other to inhibit activin signaling. The potentiation of TGF� signaling by betaglycan is thought to arise from its ability to bind and localize TGF� ligands on the cell surface. To investigate this, we will determine the structures of betaglycan's two independent TGF� binding domains, BGE and BGU, bound to TGF� using crystallography, which is ideal for these purposes, as BGE and BGU bind and form highly stable complexes with TGF�. The mechanisms for potentiation of receptor binding suggested by the structure of the complexes will be tested in functional assays. The inhibition of activin signaling by betaglycan is thought t be mediated by sequestration of the activin type II receptor, ActRII or the close homolog ActRIIb, in a ternary complex with betaglycan and inhibin A, a heterodimeric ligand with an activin � subunit that binds the activin type II receptor, ActRII/ActRIIb, and an activin � subunit that binds BGU, betaglycan's C-terminal binding domain. To investigate this, we will first determine how activins bind their type I receptor, ActRIb. These studies will be carried out using NMR as ActRIb binds activin A weakly. This will be further investigated by determining the structure of inhibin A bound to BGU using crystallography, which is ideal for these purposes as BGU binds and forms a highly stable complex with inhibin A. The mechanisms for antagonism of activin by inhibin A suggested by the structure of the complexes will be tested in functional assays. The feasibility of the proposed studies is demonstrated by diffracting crystals obtained for the BGE:T�RII:TGF� complex, the ability to isolate the BGUC:TGF� complex, and NMR signal assignments for ActRIb. The determination of these structures will provide an important missing link in our understanding of how one of the accessory proteins of the superfamily, betaglycan, influences downstream signaling induced by TGF�s and activin. The structures will also aid in the development of novel targeted-therapies for treatment of diseases and disorders, such as cancer and infertility, caused by aberrant TGF� and activin signaling.