At5g50600 encodes a member of the short-chain dehydrogenase reductase superfamily with 11beta- and 17beta-hydroxysteroid dehydrogenase activities associated with Arabidopsis thaliana seed oil bodies

• Published in: Biochimie Vol. 89; no. 2; p. 222
• Main Authors: d'Andréa, S, Canonge, M, Beopoulos, A, Jolivet, P, Hartmann, M A, Miquel, M, Lepiniec, L, Chardot, T
• Format: Journal Article
• Language: English
• Published: France 01.02.2007
• Subjects: 17-Hydroxysteroid Dehydrogenases - genetics; 17-Hydroxysteroid Dehydrogenases - metabolism; Amino Acid Sequence; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Electrophoresis, Polyacrylamide Gel; Estradiol - metabolism; Fatty Acid Synthases - genetics; Fatty Acid Synthases - metabolism; Kinetics; Molecular Sequence Data; NADH, NADPH Oxidoreductases - genetics; NADH, NADPH Oxidoreductases - metabolism; NADP - metabolism; Oxidation-Reduction; Phylogeny; Plant Oils - metabolism; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Seeds - genetics; Seeds - metabolism; Sequence Alignment; Substrate Specificity
• ISSN: 0300-9084
• DOI: 10.1016/j.biochi.2006.09.013

In a previous work, we presented evidence for the presence of a protein encoded by At5g50600 in oil bodies (OBs) from Arabidopsis thaliana [P. Jolivet, E. Roux, S. D'Andrea, M. Davanture, L. Negroni, M. Zivy, T. Chardot, Protein composition of oil bodies in Arabidopsis thaliana ecotype WS, Plant Physiol. Biochem. 42 (2004) 501-509]. Using specific antibodies and proteomic techniques, we presently confirm the existence of this protein, which is a member of the short-chain steroid dehydrogenase reductase superfamily. We have measured its activity toward various steroids (cholesterol, dehydroepiandrosterone, cortisol, corticosterone, estradiol, estrone) and NAD(P)(H), either within purified OBs or as a purified bacterially expressed chimera. Both enzymatic systems (OBs purified from A. thaliana seeds as well as the chimeric enzyme) exhibited hydroxysteroid dehydrogenase (HSD) activity toward estradiol (17beta-hydroxysteroid) with NAD+ or NADP+, NADP+ being the preferred cofactor. Low levels of activity were observed with cortisol or corticosterone (11beta-hydroxysteroids), but neither cholesterol nor DHEA (3beta-hydroxysteroids) were substrates, whatever the cofactor used. Similar activity profiles were found for both enzyme sources. Purified OBs were found to be also able to catalyze estrone reduction (17beta-ketosteroid reductase activity) with NADPH. The enzyme occurring in A. thaliana OBs can be classified as a NADP+-dependent 11beta-,17beta-hydroxysteroid dehydrogenase/17beta-ketosteroid reductase. This enzyme probably corresponds to AtHSD1, which is encoded by At5g50600. However, its physiological role and substrates still remain to be determined.