Alpha-retinals as rhodopsin chromophores--preference for the 9-Z configuration and partial agonist activity.
Photochem Photobiol
; 84(4): 889-94, 2008.
Article
em En
| MEDLINE
| ID: mdl-18346085
ABSTRACT
The visual pigment rhodopsin, the photosensory element of the rod photoreceptor cell in the vertebrate retina, shows in combination with an endogenous ligand, 11-Z retinal, an astonishing photochemical performance. It exhibits an unprecedented quantum yield (0.67) in a highly defined and ultrafast photoisomerization process. This triggers the conformational changes leading to the active state Meta(rhodopsin) II. Retinal is covalently bound to Lys-296 of the protein opsin in a protonated Schiff base. The resulting positive charge delocalization over the terminal part of the polyene chain of retinal creates a conjugation defect that upon photoexcitation moves to the opposite end of the polyene. Shortening the polyene as in 4,5-dehydro,5,6-dihydro (alpha), 5,6-dihydro or 7,8-dihydro-analogs might facilitate photoisomerization of a 9-Z and a 11-Z bond. Here we describe pigment analogs generated with bovine opsin and 11-Z or 9-Z 4,5-dehydro,5,6-dihydro-retinal that were further characterized by UV-Vis and FTIR spectroscopy. The preference of opsin for native 11-Z retinal over the 9-Z isomer is reversed in 4,5-dehydro,5,6-dihydro-retinal. 9-Z 4,5-dehydro,5,6-dihydro-retinal readily generated a photosensitive pigment. This modification has no effect on the quantum yield, but affects the Batho<-->blueshifted intermediate (BSI) equilibrium and leads to a strong decrease in the G-protein activation rate because of a downshift of the pK(a) of the Meta I<-->Meta II equilibrium.
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Retinaldeído
/
Rodopsina
Idioma:
En
Revista:
Photochem Photobiol
Ano de publicação:
2008
Tipo de documento:
Article
País de afiliação:
Holanda