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2VDG is a 1 chain structure of sequence

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Template:STRUCTURE 2VDG

BARLEY ALDOSE REDUCTASE 1 COMPLEX WITH BUTANOL


Cytokinin deshydrogenase(Wikipedia), also called CKX, is an enzyme which degrades cytokinin (Wikipedia) hormones in plants and which is encoded by the gene ZmCKX1. The one is located in Zea Maize on the chromosome 3 (NCBI Gene ID: 542585) and belongs to a multigene family called Vanillyl-Alcohol Oxidase (VAO) flavoprotein family. The gene is more particularly expressed in the kernel of maize, mainly in the embryo since it may protect the embryo from too much cytokinin and permit the correct development. [1]

Cytokine deshydrogenase are extracellular and monomeric proteins with a molecular weight of 63kDa.[2][3] For protein production purposes, ZmCKO1 precursor protein was truncated by deletion of 18 N-terminal amino acids to produce the expected mature enzyme. [4] The Enzyme Classification number of CKX is EC 1.5.99.12 and this indicates that the enzyme is an oxydo reductase which acts on the CH-NH group of the donor. Consequently the reaction of CKX with its cytokinin substrate is a transfer of two electrons from the cytokinin to an electron acceptor which is in the case of CKX the Flavine Adenine Nucleotide (FAD) cofactor. [2]

In some papers the denomination CKO can be found for cytokinin deshydrogenase. Indeed in the vanillyl-alcohol oxidase flavoprotein family most of the enzyme use molecular oxygen as electron acceptor to reoxidize the FAD cofactor. That’s why the enzyme was first called Cytokinin Oxidase (CKO). CKX is an exception in the family since the enzyme uses other compounds ,such as quinone, for electron acceptor and poorly reacts with oxygen. Consequently the enzyme is now called CKX and enters the category of dehydrogenase. [1] [5]

Structure & Function

Motifs & Domains

CKX has a two main domains structure, with an FAD-binding domain (residues 33–244 and 492–534) and a substrate-binding domain (residues 245–491). [2] The active site contains very highly conserved residues except for one residue which is located at the entrance of the active site (where a few amino acids such as Glu, Asp, Ser, Gly and other aliphatic amino acids can be found). [2] Three residues, Asp169, Glu288 and Glu381 may have an importance in cytokinin binding and enzyme action [4] The presence of a conserved �GHS� at position 104-106 domain has been shown in the FAD binding domain which may have been highlighted in CKX structure like GlWeVPHPWLNL motif around position 390 and PGQxIF signature at the C-terminal ends. These sequences are specifically found in CKX family enzymes and their very high conservation inside the family shows that they have an important role for the enzyme functioning, such as in this case substrate recognition and electron transport. [6]

References

  1. ↑ 1.0 1.1 Frebortova J, Novak O, Frebort I, Jorda R. Degradation of cytokinins by maize cytokinin dehydrogenase is mediated by free radicals generated by enzymatic oxidation of natural benzoxazinones. Plant J. 2010 Feb 1;61(3):467-81. doi: 10.1111/j.1365-313X.2009.04071.x. Epub, 2009 Nov 14. PMID:19912568 doi:http://dx.doi.org/10.1111/j.1365-313X.2009.04071.x
  2. ↑ 2.0 2.1 2.2 2.3 Kopecny D, Briozzo P, Popelkova H, Sebela M, Koncitikova R, Spichal L, Nisler J, Madzak C, Frebort I, Laloue M, Houba-Herin N. Phenyl- and benzylurea cytokinins as competitive inhibitors of cytokinin oxidase/dehydrogenase: a structural study. Biochimie. 2010 Aug;92(8):1052-62. Epub 2010 May 15. PMID:20478354 doi:10.1016/j.biochi.2010.05.006
  3. ↑ Kopecny D, Sebela M, Briozzo P, Spichal L, Houba-Herin N, Masek V, Joly N, Madzak C, Anzenbacher P, Laloue M. Mechanism-based inhibitors of cytokinin oxidase/dehydrogenase attack FAD cofactor. J Mol Biol. 2008 Jul 25;380(5):886-99. Epub 2008 May 24. PMID:18571199 doi:10.1016/j.jmb.2008.05.044
  4. ↑ 4.0 4.1 Kopecny D, Pethe C, Sebela M, Houba-Herin N, Madzak C, Majira A, Laloue M. High-level expression and characterization of Zea mays cytokinin oxidase/dehydrogenase in Yarrowia lipolytica. Biochimie. 2005 Nov;87(11):1011-22. PMID:15927342 doi:http://dx.doi.org/10.1016/j.biochi.2005.04.006
  5. ↑ Malito E, Coda A, Bilyeu KD, Fraaije MW, Mattevi A. Structures of Michaelis and product complexes of plant cytokinin dehydrogenase: implications for flavoenzyme catalysis. J Mol Biol. 2004 Aug 27;341(5):1237-49. PMID:15321719 doi:http://dx.doi.org/10.1016/j.jmb.2004.06.083
  6. ↑ Schmulling T, Werner T, Riefler M, Krupkova E, Bartrina y Manns I. Structure and function of cytokinin oxidase/dehydrogenase genes of maize, rice, Arabidopsis and other species. J Plant Res. 2003 Jun;116(3):241-52. Epub 2003 Apr 29. PMID:12721786 doi:http://dx.doi.org/10.1007/s10265-003-0096-4
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