title: Biochemical characterization of TASSELSEED 2, an essential plant short-chain dehydrogenase/reductase with broad spectrum activities.
abstract: The development of unisexual flowers in maize and other plants proceeds through selective elimination of floral organs in an initially bisexual floral meristem. The essential character of the tasselseed 2 gene (TS2) in this cell-death pathway has been established previously. Molecular cloning of TS2 reveals membership to the evolutionarily conserved superfamily of short-chain dehydrogenases/reductases, but its substrate specificity remained unknown. Recombinant TS2 protein was produced in Escherichia coli, and purified to apparent homogeneity. Analytical ultracentrifugation and gel filtration experiments show that TS2 is a tetrameric enzyme. Thermal denaturation followed by circular dichroism spectroscopy reveals that TS2 binds NAD(H) and NAD(P)(H). Substrate screening demonstrates that TS2 converts steroids with specificities found at positions 3 and 17, and several dicarbonyl and quinone compounds, thus establishing TS2 as a plant 3beta/17beta-hydroxysteroid dehydrogenase and carbonyl/quinone reductase. Taken together, the genetic data and the substrate specificities determined suggest that TS2 converts specific plant compounds and acts as a prereceptor control mechanism, in a manner similar to that of mammalian hydroxysteroid dehydrogenases.
authors.affiliation: Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Xiaoqiu
authors.initials: X
authors.lastname: Wu
authors.forename: Stefan
authors.initials: S
authors.lastname: Knapp
authors.forename: Anna
authors.initials: A
authors.lastname: Stamp
authors.forename: David K
authors.initials: DK
authors.lastname: Stammers
authors.forename: Hans
authors.initials: H
authors.lastname: Jörnvall
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Dellaporta
authors.forename: Udo
authors.initials: U
authors.lastname: Oppermann
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D006913:Hydroxysteroid Dehydrogenases / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010944:Plants / Q000201:enzymology* / Q000235:genetics; D011489:Protein Denaturation; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D008024:Ligands; D010940:Plant Proteins; D011994:Recombinant Proteins; D009243:NAD; D009249:NADP; D006913:Hydroxysteroid Dehydrogenases