title: Partial agonism in a G Protein-coupled receptor: role of the retinal ring structure in rhodopsin activation.
abstract: The visual process in rod cells is initiated by absorption of a photon in the rhodopsin retinal chromophore and consequent retinal cis/trans-isomerization. The ring structure of retinal is thought to be needed to transmit the photonic energy into conformational changes culminating in the active metarhodopsin II (Meta II) intermediate. Here, we demonstrate that cis-acyclic retinals, lacking four carbon atoms of the ring, can activate rhodopsin. Detailed analysis of the activation pathway showed that, although the photoproduct pathway is more complex, Meta II formed with almost normal kinetics. However, lack of the ring structure resulted in a low amount of Meta II and a fast decay of activity. We conclude that the main role of the ring structure is to maintain the active state, thus specifying a mechanism of activation by a partial agonist of the G protein-coupled receptor rhodopsin.
authors: Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, Schumannstrasse 20/21, D-10098 Berlin, Germany. franx.bartl@charite.de
authors: Franz J
authors: FJ
authors: Bartl
authors: Olaf
authors: O
authors: Fritze
authors: Eglof
authors: E
authors: Ritter
authors: Rolf
authors: R
authors: Herrmann
authors: Vladimir
authors: V
authors: Kuksa
authors: Krzysztof
authors: K
authors: Palczewski
authors: Klaus Peter
authors: KP
authors: Hofmann
authors: Oliver P
authors: OP
authors: Ernst
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D007536:Isomerism; D007700:Kinetics; D043562:Receptors, G-Protein-Coupled / Q000819:agonists* / Q000502:physiology*; D012160:Retina / Q000502:physiology / Q000648:ultrastructure*; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology; D012172:Retinaldehyde / Q000378:metabolism; D012243:Rhodopsin / Q000378:metabolism*; D017299:Rod Opsins / Q000378:metabolism
chemical_list: D043562:Receptors, G-Protein-Coupled; D017299:Rod Opsins; C013110:metarhodopsins; D012243:Rhodopsin; D012172:Retinaldehyde