title: High-level expression and characterization of Zea mays cytokinin oxidase/dehydrogenase in Yarrowia lipolytica.
abstract: Cytokinin oxidase/dehydrogenase (CKO/CKX) is a flavoenzyme, which irreversibly inactivates cytokinins by severing the isoprenoid side chain from the adenine/adenosine moiety. There are several genes coding for the enzyme in maize (Zea mays). A Z. mays CKO1 cDNA was cloned in the yeast Yarrowia lipolytica to achieve heterologous protein expression. The recombinant ZmCKO1 was recovered from cultures of transformed yeasts and purified using several chromatographic steps. The enzyme was obtained as a homogeneous protein in a remarkably high-yield and its molecular and kinetic properties were characterized. The enzyme showed a molecular mass of 69 kDa, pI was 6.3. Neutral sugar content of the molecule was 22%. Absorption and fluorescence spectra were in accordance with the presence of FAD as a cofactor. Peptide mass fingerprinting using MALDI-MS correctly assigned the enzyme in MSDB protein database. The enzyme showed a relatively high degree of thermostability (T50=55 degrees C for 30 min incubation). The following pH optimum and K(m) values were determined for natural substrates (measured in the oxidase mode): pH 8.0 for isopentenyl adenine (K(m)=0.5 microM), pH 7.6 for isopentenyl adenosine (K(m)=1.9 microM), pH 7.9 for zeatin (K(m)=1.5 microM) and pH 7.3 for zeatin riboside (K(m)=2.0 microM). ZmCKO1, functioning in the oxidase mode, catalyzes the production of one molecule of H2O2 per one molecule of cytokinin substrate. This finding represents clear evidence for the existence of dual enzyme functionality (oxygen serves as a cosubstrate in the absence of better electron acceptors).
authors.affiliation: Laboratoire de Biologie Cellulaire, INRA, Route de Saint-Cyr, 78026 Versailles cedex, France.
authors.forename: David
authors.initials: D
authors.lastname: Kopecný
authors.forename: Claude
authors.initials: C
authors.lastname: Pethe
authors.forename: Marek
authors.initials: M
authors.lastname: Sebela
authors.forename: Nicole
authors.initials: N
authors.lastname: Houba-Hérin
authors.forename: Catherine
authors.initials: C
authors.lastname: Madzak
authors.forename: Amel
authors.initials: A
authors.lastname: Majira
authors.forename: Michel
authors.initials: M
authors.lastname: Laloue
mesh_terms: D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D003001:Cloning, Molecular; D006861:Hydrogen Peroxide / Q000378:metabolism; D007526:Isoelectric Point; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010088:Oxidoreductases / Q000096:biosynthesis* / Q000302:isolation & purification* / Q000378:metabolism; D010449:Peptide Mapping; D011994:Recombinant Proteins / Q000302:isolation & purification; D013050:Spectrometry, Fluorescence; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013056:Spectrophotometry, Ultraviolet; D025062:Yarrowia / Q000201:enzymology*; D003313:Zea mays / Q000201:enzymology*
chemical_list: D011994:Recombinant Proteins; D006861:Hydrogen Peroxide; D010088:Oxidoreductases; C019984:cytokinin oxidase