title: Influence of the cis-9, cis-12 and cis-15 double bond position in octadecenoic acid (18:1) isomers on the rat FADS2-catalyzed Δ6-desaturation.
abstract: Oleic (cis9-18:1), linoleic (cis9,cis12-18:2) and α-linolenic (cis9,cis12,cis15-18:3) acids are well described substrates of the Δ6-desaturase encoded by the mammalian fatty acid desaturase 2 (FADS2) gene. In addition, at least 9 other very structurally different fatty acids have been shown to be Δ6- or even Δ8-desaturated by the FADS2 protein. A better characterization of the substrate specificity of this enzyme is therefore needed. By using commercial cis9-18:1 and chemically synthesized cis12- and cis15-18:1 (sharing the n-6 double bond with 18:2 n-6 and the n-3 double bond with 18:3 n-3, respectively), we tried to decrypt the fatty acid structure driving the FADS2 substrate affinity. We first showed that both recombinant and native rat FADS2 were able to Δ6-desaturate not only the cis9- but also the cis12- and cis15-18:1 isomers. Next, the inhibitory effect of increasing concentrations of each 18:1 isomer was investigated in vitro on the Δ6-desaturation of α-linolenic acid. At equimolar inhibitor/substrate ratio (60 μM), the cis9-18:1 exhibited a significantly higher inhibition (25%) than the cis12- (8%) and cis15-18:1 (5%). This study shows that a single cis double bond in 12- or 15-position in 18:1 is enough to make them low Δ6-desaturable substrates. If a preexisting cis9-double bond is not absolutely required for the Δ6-desaturation of octadecenoic acids, its presence is however crucial to explain the higher enzyme affinity. Compared with oleic acid, the additional presence of a cis12-double bond in linoleic acid increased its inhibitory effect on the Δ6-desaturation of α-linolenic acid at low concentration (30 μM) but not at higher concentrations (60 and 120 μM). In this classification of the decreasing impact of the double bond when it comes closer to the methyl end of octadecenoic acids, the cis11-18:1 (cis-vaccenic acid) should be considered apart since it is itself not Δ6-desaturated but still a good competitive inhibitor of the α-linolenic acid Δ6-desaturation.
authors.affiliation: Laboratoire de Biochimie-Nutrition Humaine, Agrocampus Ouest-INRA, USC 1378, 35000 Rennes, France. Electronic address: Vincent.Rioux@agrocampus-ouest.fr.
authors.forename: Vincent
authors.initials: V
authors.lastname: Rioux
authors.affiliation: Laboratoire de Biochimie-Nutrition Humaine, Agrocampus Ouest-INRA, USC 1378, 35000 Rennes, France.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Choque
authors.affiliation: Laboratoire de Biochimie-Nutrition Humaine, Agrocampus Ouest-INRA, USC 1378, 35000 Rennes, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Ezanno
authors.affiliation: Laboratoire de Biochimie-Nutrition Humaine, Agrocampus Ouest-INRA, USC 1378, 35000 Rennes, France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Duby
authors.affiliation: Laboratoire de Biochimie-Nutrition Humaine, Agrocampus Ouest-INRA, USC 1378, 35000 Rennes, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Catheline
authors.affiliation: Laboratoire de Biochimie-Nutrition Humaine, Agrocampus Ouest-INRA, USC 1378, 35000 Rennes, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Legrand
mesh_terms: D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D004789:Enzyme Activation; D007536:Isomerism; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013229:Stearic Acids / Q000737:chemistry* / Q000378:metabolism*; D013230:Stearoyl-CoA Desaturase / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: C114874:5-octadecenoic acid; D013229:Stearic Acids; D013230:Stearoyl-CoA Desaturase; C474452:delta 6-desaturase, rat
keywords: Fatty acid desaturase 2; Monounsaturated fatty acids; Substrate specificity; Δ6-Desaturase activity