Higher-order architecture of rhodopsin in intact photoreceptors and its implication for phototransduction kinetics

  • Gunkel M
  • Schöneberg J
  • Alkhaldi W
 et al. 
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Abstract

The visual pigment rhodopsin belongs to the family of G protein-coupled receptors that can form higher oligomers. It is controversial whether rhodopsin forms oligomers and whether oligomers are functionally relevant. Here, we study rhodopsin organization in cryosections of dark-adapted mouse rod photoreceptors by cryoelectron tomography. We identify four hierarchical levels of organization. Rhodopsin forms dimers; at least ten dimers form a row. Rows form pairs (tracks) that are aligned parallel to the disk incisures. Particle-based simulation shows that the combination of tracks with fast precomplex formation, i.e. rapid association and dissociation between inactive rhodopsin and the G protein transducin, leads to kinetic trapping: rhodopsin first activates transducin from its own track, whereas recruitment of transducin from other tracks proceeds more slowly. The trap mechanism could produce uniform single-photon responses independent of rhodopsin lifetime. In general, tracks might provide a platform that coordinates the spatiotemporal interaction of signaling molecules.

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Authors

  • Monika Gunkel

  • Johannes Schöneberg

  • Weaam Alkhaldi

  • Stephan Irsen

  • Frank Noé

  • U. Benjamin Kaupp

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