Protein Domain : Rhodopsin, retinal binding site IPR018229

Type	Binding_site
Description	The bacterial opsins are retinal-binding proteins that provide light- dependent ion transport and sensory functions to a family of halophilic bacteria [ , ]. They are integral membrane proteins believed to contain seven transmembrane (TM) domains, the last of which contains the attachment point for retinal (a conserved lysine). There are several classes of these bacterial proteins: they include bacteriorhodopsin and archaerhodopsin, which are light-driven proton pumps; halorhodopsin, a light-driven chloride pump; and sensory rhodopsin, which mediates both photoattractant (in the red) and photophobic (in the UV) responses.Fungi also contain proteins with similarities to opsin. In the Neurospora crassa opsin NOP-1 the chromophore is buried in a pocket within a 7TM structure, and bound by a protonated Schiff base to a lysine. The absorption of green light leads to an all-trans isomerisation of retinal, followed by the deprotonation of the Schiff base, resulting in a near-UV-absorbing intermediate. Archaeal rhodopsins employ this mechanism in order to pump protons over the plasma membrane and act predominantly as light-driven ion transporters the reaction cycle of NOP-1 is far too long (up to seconds) to operate as an effective ion pump, suggesting rather that it has signaling functions [ ]. Deletion of nop-1 does not cause any discernible phenotype [, ].This entry contains two conserved patterns: the first pattern (BACTERIAL_OPSIN_1) corresponds to the third transmembrane region (called helix C) and includes an arginine residue which seems involved in the release of a proton from the Schiff's base to the extracellular medium, the second pattern (BACTERIAL_OPSIN_RET) includes the retinal binding lysine [].
Short Name	Rhodopsin_retinal_BS