title: Histidine-41 of the cytochrome b5 domain of the borage delta6 fatty acid desaturase is essential for enzyme activity.
abstract: Unlike most other plant microsomal desaturases, the Delta6-fatty acid desaturase from borage (Borago officinalis) contains an N-terminal extension that shows homology to the small hemoprotein cytochrome (Cyt) b5. To determine if this domain serves as a functional electron donor for the Delta6-fatty acid desaturase, mutagenesis and functional analysis by expression in transgenic Arabidopsis was carried out. Although expression of the wild-type borage Delta6-fatty acid desaturase resulted in the synthesis and accumulation of Delta6-unsaturated fatty acids, this was not observed in plants transformed with N-terminally deleted forms of the desaturase. Site-directed mutagenesis was used to disrupt one of the axial heme-binding residues (histidine-41) of the Cyt b5 domain; expression of this mutant form of the Delta6-desaturase in transgenic plants failed to produce Delta6-unsaturated fatty acids. These data indicate that the Cyt b5 domain of the borage Delta6-fatty acid desaturase is essential for enzymatic activity.
authors.affiliation: IACR-Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Bristol BS41 9AF, United Kingdom.
authors.forename: O
authors.initials: O
authors.lastname: Sayanova
authors.forename: P R
authors.initials: PR
authors.lastname: Shewry
authors.forename: J A
authors.initials: JA
authors.lastname: Napier
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015786:Cytochromes b5 / Q000737:chemistry* / Q000378:metabolism*; D044943:Fatty Acid Desaturases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006639:Histidine; D006801:Humans; D050602:Linoleoyl-CoA Desaturase; D008861:Microsomes / Q000201:enzymology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D011994:Recombinant Proteins; D006639:Histidine; D015786:Cytochromes b5; D044943:Fatty Acid Desaturases; D050602:Linoleoyl-CoA Desaturase