guanosine-triphosphate and Retinal-Degeneration

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; 3',5'-Cyclic-GMP Phosphodiesterases; Animals; Cattle; Cyclic GMP; Dog Diseases; Dogs; Guanosine Triphosphate; Guanylate Cyclase; Hydrolysis; Mice; Mice, Mutant Strains; Phosphoproteins; Photoreceptor Cells; Rabbits; Rats; Retina; Retinal Degeneration; Rod Cell Outer Segment; Rodent Diseases

Dysfunctions of primary cilia and cilia-derived sensory organelles underlie a multitude of human disorders, including retinal degeneration, yet membrane targeting to the cilium remains poorly understood. Here, we show that the newly identified ciliary targeting VxPx motif present in rhodopsin binds the small GTPase Arf4 and regulates its association with the trans-Golgi network (TGN), which is the site of assembly and function of a ciliary targeting complex. This complex is comprised of two small GTPases, Arf4 and Rab11, the Rab11/Arf effector FIP3, and the Arf GTPase-activating protein ASAP1. ASAP1 mediates GTP hydrolysis on Arf4 and functions as an Arf4 effector that regulates budding of post-TGN carriers, along with FIP3 and Rab11. The Arf4 mutant I46D, impaired in ASAP1-mediated GTP hydrolysis, causes aberrant rhodopsin trafficking and cytoskeletal and morphological defects resulting in retinal degeneration in transgenic animals. As the VxPx motif is present in other ciliary membrane proteins, the Arf4-based targeting complex is most likely a part of conserved machinery involved in the selection and packaging of the cargo destined for delivery to the cilium.

Topics: Actin Cytoskeleton; Adaptor Proteins, Signal Transducing; ADP-Ribosylation Factors; Amino Acid Motifs; Amino Acid Sequence; Animals; Animals, Genetically Modified; Cilia; GTPase-Activating Proteins; Guanosine Triphosphate; Hydrolysis; I-kappa B Kinase; Intracellular Membranes; Molecular Sequence Data; Mutant Proteins; Organ Specificity; Protein Binding; Protein Sorting Signals; Protein Structure, Tertiary; Protein Transport; rab GTP-Binding Proteins; Retinal Degeneration; Rhodopsin; trans-Golgi Network; Xenopus; Xenopus Proteins

Heterotrimeric guanosine 5'-triphosphate (GTP)-binding proteins (G proteins) are deactivated by hydrolysis of the GTP that they bind when activated by transmembrane receptors. Transducin, the G protein that relays visual excitation from rhodopsin to the cyclic guanosine 3',5'-monophosphate phosphodiesterase (PDE) in retinal photoreceptors, must be deactivated for the light response to recover. A point mutation in the gamma subunit of PDE impaired transducin-PDE interactions and slowed the recovery rate of the flash response in transgenic mouse rods. These results indicate that the normal deactivation of transducin in vivo requires the G protein to interact with its target enzyme.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Animals; Cyclic Nucleotide Phosphodiesterases, Type 6; Electroretinography; Enzyme Activation; Female; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Triphosphate; Hydrolysis; Light; Male; Mice; Mice, Knockout; Mice, Transgenic; Point Mutation; Retina; Retinal Degeneration; Rod Cell Outer Segment; Transducin; Transgenes; Vision, Ocular

Topics: Adenosine Triphosphate; Adenylyl Cyclases; Animals; Anura; Cattle; Cyclic AMP; Cyclic GMP; Guanosine Triphosphate; Guanylate Cyclase; Mice; Mice, Inbred C3H; Phosphoric Diester Hydrolases; Photoreceptor Cells; Protein Kinases; Rats; Retina; Retinal Degeneration