Ligand-receptor interactions in the TGF-beta superfamily

描述（申请人提供）：TGF - s和TGF -超家族的其他结构相关蛋白，如bmp、GDFs、激活素等，是调节许多重要过程的分泌信号蛋白，从胚胎发生时机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人类疾病所证明，这些疾病是由该途径的失调引起的，包括骨骼和心脏疾病、不孕症和癌症。治疗途径相关疾病的有效疗法的发展需要了解控制配体活性的相互作用，这包括与信号受体的相互作用，以及与许多结合配体和调节配体可及性的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

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.