3C0P image
Deposition Date 2008-01-21
Release Date 2008-07-15
Last Version Date 2024-11-13
Entry Detail
PDB ID:
3C0P
Keywords:
Title:
Maize cytokinin oxidase/dehydrogenase complexed with the allenic cytokinin analog HA-8
Biological Source:
Source Organism:
Zea mays (Taxon ID: 4577)
Host Organism:
Method Details:
Experimental Method:
Resolution:
1.95 Å
R-Value Free:
0.24
R-Value Work:
0.21
Space Group:
C 1 2 1
Macromolecular Entities
Polymer Type:polypeptide(L)
Molecule:Cytokinin dehydrogenase 1
Gene (Uniprot):CKX1
Chain IDs:A
Chain Length:516
Number of Molecules:1
Biological Source:Zea mays
Modified Residue
Compound ID Chain ID Parent Comp ID Details 2D Image
ASN A ASN GLYCOSYLATION SITE
Primary Citation
Mechanism-based inhibitors of cytokinin oxidase/dehydrogenase attack FAD cofactor
J.Mol.Biol. 380 886 899 (2008)
PMID: 18571199 DOI: 10.1016/j.jmb.2008.05.044

Abstact

Cytokinin oxidases/dehydrogenases (CKOs) mediate catabolic regulation of cytokinin levels in plants. Several substrate analogs containing an unsaturated side chain were studied for their possible inhibitory effect on maize CKO (ZmCKO1) by use of various bioanalytical methods. Two allenic derivatives, N(6)-(buta-2,3-dienyl)adenine (HA-8) and N(6)-(penta-2,3-dienyl)adenine (HA-1), were identified as strong mechanism-based inhibitors of the enzyme. Despite exhaustive dialysis, the enzyme remained inhibited. Conversely, substrate analogs with a triple bond in the side chain were much weaker inactivators. The crystal structures of recombinant ZmCKO1 complexed with HA-1 or HA-8 were solved to 1.95 A resolution. Together with Raman spectra of the inactivated enzyme, it was revealed that reactive imine intermediates generated by oxidation of the allenic inhibitors covalently bind to the flavin adenine dinucleotide (FAD) cofactor. The binding occurs at the C4a atom of the isoalloxazine ring of FAD, the planarity of which is consequently disrupted. All the compounds under study were also analyzed for binding to the Arabidopsis cytokinin receptors AHK3 and AHK4 in a bacterial receptor assay and for cytokinin activity in the Amaranthus bioassay. HA-1 and HA-8 were found to be good receptor ligands with a significant cytokinin activity. Nevertheless, due to their ability to inactivate CKO in the desired time intervals or developmental stages, they both represent attractive compounds for physiological studies, as the inhibition mechanism of HA-1 and HA-8 is mainly FAD dependent.

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