title: Interaction of glutamic-acid-rich proteins with the cGMP signalling pathway in rod photoreceptors.
abstract: The assembly of signalling molecules into macromolecular complexes (transducisomes) provides specificity, sensitivity and speed in intracellular signalling pathways. Rod photoreceptors in the eye contain an unusual set of glutamic-acid-rich proteins (GARPs) of unknown function. GARPs exist as two soluble forms, GARP1 and GARP2, and as a large cytoplasmic domain (GARP' part) of the beta-subunit of the cyclic GMP-gated channel. Here we identify GARPs as multivalent proteins that interact with the key players of cGMP signalling, phosphodiesterase and guanylate cyclase, and with a retina-specific ATP-binding cassette transporter (ABCR), through four, short, repetitive sequences. In electron micrographs, GARPs are restricted to the rim region and incisures of discs in close proximity to the guanylate cyclase and ABCR, whereas the phosphodiesterase is randomly distributed. GARP2, the most abundant splice form, associates more strongly with light-activated than with inactive phosphodiesterase, and GARP2 potently inhibits phosphodiesterase activity. Thus, the GARPs organize a dynamic protein complex near the disc rim that may control cGMP turnover and possibly other light-dependent processes. Because there are no similar GARPs in cones, we propose that GARPs may prevent unnecessary cGMP turnover during daylight, when rods are held in saturation by the relatively high light levels.
authors.affiliation: Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, Germany.
authors.forename: H G
authors.initials: HG
authors.lastname: Körschen
authors.forename: M
authors.initials: M
authors.lastname: Beyermann
authors.forename: F
authors.initials: F
authors.lastname: Müller
authors.forename: M
authors.initials: M
authors.lastname: Heck
authors.forename: M
authors.initials: M
authors.lastname: Vantler
authors.forename: K W
authors.initials: KW
authors.lastname: Koch
authors.forename: R
authors.initials: R
authors.lastname: Kellner
authors.forename: U
authors.initials: U
authors.lastname: Wolfrum
authors.forename: C
authors.initials: C
authors.lastname: Bode
authors.forename: K P
authors.initials: KP
authors.lastname: Hofmann
authors.forename: U B
authors.initials: UB
authors.lastname: Kaupp
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D006152:Cyclic GMP / Q000378:metabolism*; D054815:Cyclic Nucleotide-Gated Cation Channels; D005136:Eye Proteins / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism*; D006162:Guanylate Cyclase / Q000378:metabolism; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins; D010726:Phosphodiesterase Inhibitors / Q000378:metabolism; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism* / Q000648:ultrastructure; D011994:Recombinant Proteins / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism* / Q000648:ultrastructure; D012374:Rod Cell Outer Segment / Q000378:metabolism / Q000648:ultrastructure; D015398:Signal Transduction; D015293:Transducin / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; C034698:CNGB1 protein, Bos taurus; D054815:Cyclic Nucleotide-Gated Cation Channels; D005136:Eye Proteins; D009419:Nerve Tissue Proteins; D010726:Phosphodiesterase Inhibitors; D011506:Proteins; D011994:Recombinant Proteins; D018698:Glutamic Acid; D010727:Phosphoric Diester Hydrolases; D015293:Transducin; D006162:Guanylate Cyclase; D006152:Cyclic GMP