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

一个大的跨膜受体超家族控制细胞内的 通过催化激活多种细胞外信号， 异源三聚体GTP结合蛋白的特定类型。 如何将这些 受体促进G蛋白a亚基上的核苷酸交换， 启动信号放大是未知。 三维 Gt a亚基C末端十一肽的结构 IKENLKDCGLF，通过TRNOE光谱法测定，同时结合到 光激发视紫红质 合成的十一肽的结构 已经被质谱法证实了 视紫红质光活化 导致Gta从无序构象到 一个螺旋形的结合基序，后面是一个开放的反向的转折 以Gly 348为中心，是aL型的螺旋终止C-加帽基序。 Gt的NMR结构与GDP结合的X射线结构的对接 揭示了光激发的视紫红质促进了 C-末端终止的残基325-346上的连续螺旋 螺旋帽与一个独特的关键疏水侧链集群。 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 界面展示。

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.