title: Retinal targets for calmodulin include proteins implicated in synaptic transmission.
abstract: Ca2+ influxes regulate multiple events in photoreceptor cells including phototransduction and synaptic transmission. An important Ca2+ sensor in Drosophila vision appears to be calmodulin since a reduction in levels of retinal calmodulin causes defects in adaptation and termination of the photoresponse. These functions of calmodulin appear to be mediated, at least in part, by four previously identified calmodulin-binding proteins: the TRP and TRPL ion channels, NINAC and INAD. To identify additional calmodulin-binding proteins that may function in phototransduction and/or synaptic transmission, we conducted a screen for retinal calmodulin-binding proteins. We found eight additional calmodulin-binding proteins that were expressed in the Drosophila retina. These included six targets that were related to proteins implicated in synaptic transmission. Among these six were a homolog of the diacylglycerol-binding protein, UNC13, and a protein, CRAG, related to Rab3 GTPase exchange proteins. Two other calmodulin-binding proteins included Pollux, a protein with similarity to a portion of a yeast Rab GTPase activating protein, and Calossin, an enormous protein of unknown function conserved throughout animal phylogeny. Thus, it appears that calmodulin functions as a Ca2+ sensor for a broad diversity of retinal proteins, some of which are implicated in synaptic transmission.
authors.affiliation: Departments of Biological Chemistry and Neuroscience, The Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: X Z
authors.initials: XZ
authors.lastname: Xu
authors.forename: P D
authors.initials: PD
authors.lastname: Wes
authors.forename: H
authors.initials: H
authors.lastname: Chen
authors.forename: H S
authors.initials: HS
authors.lastname: Li
authors.forename: M
authors.initials: M
authors.lastname: Yu
authors.forename: S
authors.initials: S
authors.lastname: Morgan
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.forename: C
authors.initials: C
authors.lastname: Montell
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000302:isolation & purification; D002148:Calmodulin-Binding Proteins / Q000235:genetics / Q000302:isolation & purification*; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000302:isolation & purification; D017124:Conserved Sequence; D004330:Drosophila / Q000502:physiology*; D029721:Drosophila Proteins; D019204:GTP-Binding Proteins / Q000235:genetics; D017344:Genes, Insect; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000302:isolation & purification; D012160:Retina / Q000502:physiology*; D012641:Selection, Genetic; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D009435:Synaptic Transmission / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases; D020692:rab3 GTP-Binding Proteins
chemical_list: D002148:Calmodulin-Binding Proteins; D015815:Cell Adhesion Molecules; D029721:Drosophila Proteins; D012333:RNA, Messenger; C099771:plx protein, Drosophila; D044767:Ubiquitin-Protein Ligases; C115917:poe protein, Drosophila; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D020692:rab3 GTP-Binding Proteins