Summary The Mechanism of Rhodopsin Activation and Future Directions

Summary The Mechanism of Rhodopsin Activation and Future Directions 

The focus of this review has been on rhodopsin structure and dynamics at the cytoplasmic face in solution, the comparison between the solution structure and the crystal structure, and the structural changes underlying receptor activation. The data from SDSL and disulfide cross-linking together indicate that the crystal and solution structures are very similar at the level of the backbone fold for Cl, H8, and the cytoplasmic termination of TM1-TM7. However, substantial differences are seen in C3 and the C-terminal tail, wherein the backbones are flexible on the nanosecond time scale in solution. Not surprisingly, these are the most disordered regions in the crystal lattice and correspond to sequences important for function. 

Two independent strategies, modulation of tertiary contact interaction and direct distance mapping, provide compelling evidence for a dominant rigid-body movement of TM6 near the cytoplasmic surface, with smaller but significant movements of TM1, TM2, TM3, and TM7. 

The pattern of helix motions observed experimentally suggests a simple model for the activated state in which helices on opposite sides of the chromophore binding pocket move outward to open a cleft in the molecule (Fig. 20). In the prose of Henry Bourne, the molecule has blossomed (Meng and Bourne, 2001) to expose new surfaces for coupling of rhodopsin with transducin. 

and Szuts, E. Z. (1982). Photoreceptors Their Role in Vision. Cambridge University Press, Cambridge, UK. 

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VI. Summary The Mechanism of Rhodopsin Activation and Future Directions. 285... 

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