Structural insights into the unique activation mechanisms of receptor tyrosine kinases

受体酪氨酸激酶（RTK）在调节正常细胞过程中起关键作用，并与许多细胞因子相关。 人类疾病。每个RTK原聚体含有结合活化配体的细胞外区域， 跨膜螺旋，和含有细胞内激酶结构域所必需的细胞内区域， 信号对于许多RTK，它们的同源配体形成稳定的同源二聚体，并且二聚体配体与RTK的结合不稳定。 RTK的细胞外区域驱动受体二聚化，然后使两种细胞内激酶靠近 接近，使其自身磷酸化。磷酸化激酶可以进一步募集效应蛋白， 从而触发下游信号级联。这种“配体诱导的二聚化”是长期存在的 RTKs的激活模型，并已充分表征了广泛的结构和功能 问题研究然而，有人建议RTK家族中的几个成员使用唯一激活 机制等例如，单独的MuSK受体不能直接结合其配体并被其激活， 聚集蛋白，但需要肌肉细胞表面上的辅助受体Lrp 4的辅助来激活。此外该 TAM受体的激活不仅需要其配体的结合，而且还需要 磷脂酰丝氨酸脂质（PtdSer）。此外，我们的初步结构结果 表明，与所有其他RTK不同，一个HGF分子可以同时接合两个c-MET受体 通过利用两个不同的界面;因此，单一HGF足以激活c-MET受体， 这代表了RTK激活机制的另一种范例。该项目的目标是研究 几种特殊的RTKs，包括MuSK，TAM和c-MET受体的结构和功能， 激活机制仍然知之甚少。解决不同独特的高分辨率结构 配体结合活性状态的RTK家族成员将解释区分这些的具体特征。 受体之间的相互作用，揭示了RTK激活的共同机制和多样性。 目的1：对MuSK受体复合物进行结构和功能分析。本研究将 揭示MuSK、Lrp 4和聚集蛋白之间的详细结合模式，并解释为什么辅助受体Lrp 4是关键的 用于激活MuSK。目的二是对TAM受体进行生物化学和结构分析， 膜相关功能状态。这项研究的结果将使我们能够解释功能性 PtdSer在TAM活化中重要性。目标3将集中于c-MET的结构测定 受体处于HGF结合活性状态，以了解为什么单个HGF分子足以用于c-MET activation.

Receptor tyrosine kinases (RTKs) play key roles in regulating normal cellular processes and are linked to many human diseases. Each RTK protomer contains an extracellular region that binds activating ligands, a single transmembrane helix, and an intracellular region that contains the kinase domain necessary for intracellular signaling. For many RTKs, their cognate ligands form stable homodimers, and the binding of dimeric ligand to the extracellular region of RTK drives receptor dimerization, which then brings two intracellular kinases in close proximity, enabling their autophosphorylation. The phosphorylated kinases can further recruit effector proteins, and thereby triggering downstream signaling cascade. This “ligand-induced-dimerization” is the long-standing model for the activation of RTKs, and has been well characterized by extensive structural and functional studies. Nevertheless, it has been suggested that several members in RTK family use unique activation mechanisms. For instance, the MuSK receptor alone cannot directly bind to and be activated by its ligand Agrin, but requiring assistance of the co-receptor Lrp4 on the muscle cell surface for activation. In addition, the activation of TAM receptor requires not only the binding of its ligands, but also the involvement of phosphatidylserine lipid (PtdSer) from plasma membrane. Furthermore, our preliminary structure results showed that, different to all other RTKs, one HGF molecular can simultaneously engages two c-MET receptors by utilizing two distinct interfaces; therefore, a single HGF is sufficient for the activation of c-MET receptor, which represents another paradigm in activation mechanisms of RTK. The goal of this project is to study the structures and functions of several special RTKs, including MuSK, TAM and c-MET receptors, whose activation mechanism are still poorly understood. Solving the high-resolution structures of different unique members of RTK family in the ligand-bound active state will explain the specific features that differentiate these receptors from other RTKs, and reveal the common mechanism and diversification in the activation of RTK. Aim 1 will be focused on the functional and structural analyses of MuSK receptor complex. This study will reveal the detailed binding mode between MuSK, Lrp4 and Agrin, and explain why co-receptor Lrp4 is critical for the activation of MuSK. Aim 2 will be focused on biochemical and structural analyses of TAM receptor in the membrane associated functional state. The result from this study will allow us to explain the functional importance of PtdSer in TAM activation. Aim 3 will be focused on the structural determination of c-MET receptor in the HGF bound active state to understand why single HGF molecular is sufficient for c-MET activation.