The @entity24101 @entity8695 contains a pocket within its seven-transmembrane helix (TM) structure, which bears the inactivating @entity5995 bound by a protonated @entity3364 to Lys296 in TM7. Light-induced 11-cis-/all-trans-isomerization leads to the @entity3364 deprotonated active Meta II intermediate. With Meta II decay, the @entity3364 bond is hydrolyzed, @entity31643 is released from the pocket, and the apoprotein opsin reloaded with new @entity5995 . The crystal structure of opsin in its active Ops* conformation provides the basis for computational modeling of @entity5995 release and uptake. The ligand-free 7TM bundle of opsin opens into the hydrophobic membrane layer through openings A (between @entity26381 and 7), and B (between @entity16544 ), respectively. Using skeleton search and molecular docking, we find a continuous channel through the protein that connects these two openings and comprises in its central part the retinal binding pocket. The channel traverses the receptor over a distance of ca. 70 A and is between 11.6 and 3.2 A wide. Both openings are lined with aromatic residues, while the central part is highly polar. Four constrictions within the channel are so narrow that they must stretch to allow passage of the retinal @entity31391 -ring. Constrictions are at openings A and B, respectively, and at Trp265 and Lys296 within the retinal pocket. The @entity376 enforces a 90 degrees elbow-like kink in the channel which limits retinal passage. With a favorable Lys side chain conformation, @entity5995 can take the turn, whereas passage of the all-trans isomer would require more global conformational changes. We discuss possible scenarios for the uptake of 11-cis- and release of @entity31643 . If the uptake gate of @entity5995 is assigned to opening B, all-trans is likely to leave through the same gate. The unidirectional passage proposed previously requires uptake of @entity5995 through A and release of photolyzed @entity31643 through B.

A ligand channel through the XXXX opsin.

@entity26381 :: ('MESH:C098227', 'Chemical') :: ['TM1'] @entity24101 :: ('10663', 'Gene') :: ['G protein coupled receptor'] @entity8695 :: ('6010', 'Gene') :: ['rhodopsin'] @entity3364 :: ('MESH:D012545', 'Chemical') :: ['Schiff-base'] @entity376 :: ('CHEBI:25094', 'Chemical') :: ['lysine'] @entity31391 :: ('MESH:C008157', 'Chemical') :: ['beta-ionone'] @entity5995 :: ('MESH:D012172', 'Chemical') :: ['11-cis-retinal', 'retinal'] @entity16544 :: ('7170', 'Gene') :: ['TM5 and 6'] @entity31643 :: ('CHEBI:17898', 'Chemical') :: ['all-trans-retinal']
@entity24101 :: (10663,Gene) :: ['G protein coupled receptor']
