title: The role of Drosophila ninaG oxidoreductase in visual pigment chromophore biogenesis.
abstract: We previously reported (Sarfare, S., Ahmad, S. T., Joyce, M. V., Boggess, B., and O'Tousa, J. E. (2005) J. Biol. Chem. 280, 11895-11901) that the Drosophila ninaG gene encodes an oxidoreductase involved in the biosynthesis of the (3S)-3-hydroxyretinal serving as chromophore for Rh1 rhodopsin and that ninaG mutant flies expressing Rh4 as the major opsin accumulate large amounts of a different retinoid. Here, we show that this unknown retinoid is 11-cis-3-hydroxyretinol. Reversed phase high performance liquid chromatography coupled with a photodiode array UV-visible absorbance detector and mass spectrometer revealed a major product eluting at a retention time, t(r), of 3.5 min with a lambda(max) of approximately 324 nm and with a base peak in the mass spectrum at m/z 285. These observations are identical with those of the 3-hydroxyretinol standard. The base peak in the electrospray ionization mass spectrum arises from the loss of a water molecule from the protonated molecule at m/z 303 because of fragmentation in the ion source. These results suggest that 11-cis-3-hydroxyretinol is an intermediate required for chromophore biogenesis in Drosophila. We further show that ninaG mutants fed on retinal as the sole source of vitamin A are able to synthesize 3-hydroxyretinoids. Thus, the NinaG oxidoreductase is not responsible for the initial hydroxylation of the retinal ring but rather acts in a subsequent step in chromophore production. These data are used to review chromophore biosynthesis and propose that NinaG acts in the conversion of (3R)-3-hydroxyretinol to the 3S enantiomer.
authors.affiliation: Department of Biological Sciences, and Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: Syed Tariq
authors.initials: ST
authors.lastname: Ahmad
authors.forename: Michelle V
authors.initials: MV
authors.lastname: Joyce
authors.forename: Bill
authors.initials: B
authors.lastname: Boggess
authors.forename: Joseph E
authors.initials: JE
authors.lastname: O'Tousa
mesh_terms: D000818:Animals; D004330:Drosophila / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics / Q000502:physiology*; D006900:Hydroxylation; D007536:Isomerism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D012172:Retinaldehyde / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D014801:Vitamin A / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D014801:Vitamin A; C015943:3-hydroxyretinol; C049427:3-hydroxyretinal; C510457:NinaG protein, Drosophila; D010088:Oxidoreductases; D012172:Retinaldehyde