title: Identification of the gene encoding alkylglycerol monooxygenase defines a third class of tetrahydrobiopterin-dependent enzymes.
abstract: Alkylglycerol monooxygenase (glyceryl-ether monooxygenase, EC 1.14.16.5) is the only enzyme known to cleave the O-alkyl bond of ether lipids which are essential components of brain membranes, protect the eye from cataract, interfere or mediate signalling processes, and are required for spermatogenesis. Along with phenylalanine hydroxylase, tyrosine hydroxylase, tryptophan hydroxylase, and nitric oxide synthase, alkylglycerol monooxygenase is one of five known enzymatic reactions which depend on tetrahydrobiopterin. Although first described in 1964, no sequence had been assigned to this enzyme so far since it lost activity upon protein purification attempts. A functional library screen using pools of plasmids of a rat liver expression library transfected to CHO cells was also unsuccessful. We therefore selected human candidate genes by bioinformatic approaches and by proteomic analysis of partially purified enzyme and tested alkylglycerol monooxygenase activity in CHO cells transfected with expression plasmids. Transmembrane protein 195, a predicted membrane protein with unassigned function which occurs in bilateral animals, was found to encode for tetrahydrobiopterin-dependent alkylglycerol monooxygenase. This sequence assignment was confirmed by injection of transmembrane protein 195 cRNA into Xenopus laevis oocytes. Transmembrane protein 195 shows no sequence homology to aromatic amino acid hydroxylases or nitric oxide synthases, but contains the fatty acid hydroxylase motif. This motif is found in enzymes which contain a diiron center and which carry out hydroxylations of lipids at aliphatic carbon atoms like alkylglycerol monooxygenase. This sequence assignment suggests that alkylglycerol monooxygenase forms a distinct third group among tetrahydrobiopterin-dependent enzymes.
authors.affiliation: Division of Biological Chemistry, Biocenter, Innsbruck Medical University, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria.
authors.forename: Katrin
authors.initials: K
authors.lastname: Watschinger
authors.forename: Markus A
authors.initials: MA
authors.lastname: Keller
authors.forename: Georg
authors.initials: G
authors.lastname: Golderer
authors.forename: Martin
authors.initials: M
authors.lastname: Hermann
authors.forename: Manuel
authors.initials: M
authors.lastname: Maglione
authors.forename: Bettina
authors.initials: B
authors.lastname: Sarg
authors.forename: Herbert H
authors.initials: HH
authors.lastname: Lindner
authors.forename: Albin
authors.initials: A
authors.lastname: Hermetter
authors.forename: Gabriele
authors.initials: G
authors.lastname: Werner-Felmayer
authors.forename: Robert
authors.initials: R
authors.lastname: Konrat
authors.forename: Nicolas
authors.initials: N
authors.lastname: Hulo
authors.forename: Ernst R
authors.initials: ER
authors.lastname: Werner
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives* / Q000378:metabolism; D016466:CHO Cells; D019295:Computational Biology; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D014982:Xenopus laevis
chemical_list: D008565:Membrane Proteins; D001708:Biopterins; D006899:Mixed Function Oxygenases; C020678:glyceryl-ether monooxygenase; D000445:Aldehyde Oxidoreductases; C038828:long-chain-aldehyde dehydrogenase; C003402:sapropterin