title: The VEP1 gene (At4g24220) encodes a short-chain dehydrogenase/reductase with 3-oxo-Delta4,5-steroid 5beta-reductase activity in Arabidopsis thaliana L.
abstract: The Arabidopsis thaliana VEP1 gene product shows about 70% sequence identity to Digitalis lanata progesterone 5beta-reductase, an enzyme considered to catalyze a key step in the biosynthesis of cardiac glycosides. A. thaliana does not accumulate cardenolides but protein extracts prepared from its leaves were capable of reducing progesterone to 5beta-pregnane-3,20-dione. A full-length cDNA clone encoding a Delta(4,5)-steroid 5beta-reductase (At5beta-StR, EC 1.1.1.145/1.3.1.23), a member of the short-chain dehydrogenase/reductase (SDR) family, was isolated from A. thaliana leaves. A SphI/SalI At5beta-StR gene fragment was cloned into the pQE vector system and transformed into Escherichia coli. The gene was functionally expressed and the recombinant His-tagged fusion protein was characterized. K(m) values and specific activities for putative 3-oxo-Delta(4,5)-steroid substrates such as progesterone, cortisol, cortexone and 4-androstene-3,17-dione, and for the co-substrate NADPH were determined. Progesterone was stereo-specifically reduced to 5beta-pregnane-3,20-dione and none of the 3-oxo-Delta(5,6)-steroids tested were accepted as a substrate. The gene encoding At5beta-StR was strongly transcribed in stems and leaves. A three-dimensional model of At5beta-StR highlights a close structural similarity to the related, previously described D. lanata progesterone 5beta-reductase. This homology extends to the active site where single amino acid substitutions might be responsible for the increased catalytic efficiency of At5beta-StR when compared to the activity of the recombinant form of the D. lanata enzyme.
authors.affiliation: Lehrstuhl für Pharmazeutische Biologie, Department Biologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstrasse 5, 91058 Erlangen, Germany.
authors.forename: V
authors.initials: V
authors.lastname: Herl
authors.forename: G
authors.initials: G
authors.lastname: Fischer
authors.forename: V A
authors.initials: VA
authors.lastname: Reva
authors.forename: M
authors.initials: M
authors.lastname: Stiebritz
authors.forename: Y A
authors.initials: YA
authors.lastname: Muller
authors.forename: F
authors.initials: F
authors.lastname: Müller-Uri
authors.forename: W
authors.initials: W
authors.lastname: Kreis
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018515:Plant Leaves / Q000201:enzymology*; D016415:Sequence Alignment; D013379:Substrate Specificity
chemical_list: D029681:Arabidopsis Proteins; C458520:VEP1 protein, Arabidopsis; D010088:Oxidoreductases; C021936:3-oxo-5 beta-steroid delta 4-dehydrogenase