Leucine/Valine Residues Direct Oxygenation of Linoleic Acid by (10R)- and (8R)-Dioxygenases: Expression and site-directed mutagenesis of (10R)- dioxygenase with epoxyalcohol synthase activity
2009 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 284, no 20, 13755-13765 p.Article in journal (Refereed) Published
Linoleate (10R)-dioxygenase (10R-DOX) of Aspergillus fumigatus was cloned and expressed in insect cells. Recombinant 10R-DOX oxidized 18:2n-6 to (10R)-hydroperoxy-8(E),12(Z)-octadecadienoic acid (10R-HPODE; approximately 90%), (8R)-hydroperoxylinoleic acid (8R-HPODE; approximately 10%), and small amounts of 12S(13R)-epoxy-(10R)-hydroxy-(8E)-octadecenoic acid. We investigated the oxygenation of 18:2n-6 at C-10 and C-8 by site-directed mutagenesis of 10R-DOX and 7,8-linoleate diol synthase (7,8-LDS), which forms approximately 98% 8R-HPODE and approximately 2% 10R-HPODE. The 10R-DOX and 7,8-LDS sequences differ in homologous positions of the presumed dioxygenation sites (Leu-384/Val-330 and Val-388/Leu-334, respectively) and at the distal site of the heme (Leu-306/Val-256). Leu-384/Val-330 influenced oxygenation, as L384V and L384A of 10R-DOX elevated the biosynthesis of 8-HPODE to 22 and 54%, respectively, as measured by liquid chromatography-tandem mass spectrometry analysis. The stereospecificity was also decreased, as L384A formed the R and S isomers of 10-HPODE and 8-HPODE in a 3:2 ratio. Residues in this position also influenced oxygenation by 7,8-LDS, as its V330L mutant augmented the formation of 10R-HPODE 3-fold. Replacement of Val-388 in 10R-DOX with leucine and phenylalanine increased the formation of 8R-HPODE to 16 and 36%, respectively, whereas L334V of 7,8-LDS was inactive. Mutation of Leu-306 with valine or alanine had little influence on the epoxyalcohol synthase activity. Our results suggest that Leu-384 and Val-388 of 10R-DOX control oxygenation of 18:2n-6 at C-10 and C-8, respectively. The two homologous positions of prostaglandin H synthase-1, Val-349 and Ser-353, are also critical for the position and stereospecificity of the cyclooxygenase reaction.
Place, publisher, year, edition, pages
2009. Vol. 284, no 20, 13755-13765 p.
IdentifiersURN: urn:nbn:se:uu:diva-103259DOI: 10.1074/jbc.M808665200ISI: 000265877300053PubMedID: 19289462OAI: oai:DiVA.org:uu-103259DiVA: diva2:217848