LIGHT ACTIVATED RHODOPSIN ON STRUCT BINDING MOTIF IN G PROTEIN ALPHA SUBUNIT

一个控制细胞的跨膜受体超家族 对多种细胞外信号的反应通过催化激活 特定类型的异源三聚体GTP结合蛋白。这些是如何 受体促进G蛋白a亚基上的核苷酸交换以 启动信号放大未知。三度空间 GTAα-亚基C-末端十一肽的结构 IKENLKDCGLF结合时用TRNOE光谱测定 光激发的视紫红质。人工合成十一肽的结构 经质谱学证实。视紫红质的光激活 导致从GTA的无序构象到 带有螺旋旋转和开放反向旋转的装订主题 以Gly348为中心，为al-型的螺旋末端C-帽基序。 核磁共振结构与GT的GDP结合X射线结构的对接 揭示了光激发的视紫红质促进了 C末端终止的325-346t残基上的连续螺旋 螺旋帽具有一簇独特的关键疏水侧链。 激活受体控制G蛋白的分子机制 通过受体-G蛋白的可逆构象变化 对界面进行了演示。

A large super-family of trans-membrane receptors control cellular responses to diverse extracellular signals by catalyzing activation of specific types of hetero-trimeric GTP-binding proteins. How these receptors promote nucleotide exchange on G-protein a-subunits to initiate signal amplification is unknown. The three-dimensional structure of the Gt a-subunit C-terminal undecapeptide, Gta IKENLKDCGLF, was determined by TRNOE spectroscopy while bound to photo-excited rhodopsin. The structure of the synthetic undecapeptide was confirmed by mass spectrometry. Light-activation of rhodopsin causes a dramatic shift from a disordered conformation of Gta to a binding motif with a helical turn followed by an open reverse turn centered at Gly348, a helix-terminating C-capping motif of an aL-type. Docking of the NMR structure to the GDP-bound X-ray structure of Gt reveals that photo-excited rhodopsin promotes the formation of a continuous helix over residues 325-346 t erminated by the C-terminal helical cap with a unique cluster of crucial hydrophobic side chains. A molecular mechanism by which activated receptors control G-proteins through reversible conformational changes at the receptor-G protein interface is demonstrated.