KOPEČNÝ, D., BRIOZZO, P., POPELKOVÁ, H., ŠEBELA, M., KONČITÍKOVÁ, R., SPÍCHAL, Lukáš, NISLER, Jaroslav, MADZAK, C., FRÉBORT, Ivo, LALOUE, M., HOUBA-HERIN, N. Phenyl- and benzylurea cytokinins as competitive inhibitors of cytokinin oxidase/dehydrogenase: a structural study. Biochimie. 2010, 92(8), 1052-1062. ISSN 0300-9084. E-ISSN 1638-6183

Cytokinin oxidase/dehydrogenase (CKO) is a flavoenzyme, which irreversibly degrades the plant hormones cytokinins. An inhibitory study with numerous urea derivatives was undertaken using the maize enzyme (ZmCKO1) and the crystal structure of ZmCKO1 in a complex with N-(2-chloro-pyridin-4-yl)-N´-phenylurea (CPPU) was solved. Subsequently, site-directed mutagenesis of L492 and E381 residues involved in the inhibitor binding was performed. The crystal structures of L492A mutant in a complex with CPPU and N-(2-chloro-pyridin-4-yl)-N´-benzylurea (CPBU) were solved and confirm the importance of a stacking interaction between the 2-chloro-4-pyridinyl ring of the inhibitor and the isoalloxazine ring of the FAD cofactor. As highly specific CKO inhibitors without undesired side effects are of major interest for physiological studies, all studied compounds were further analyzed for cytokinin activity in the Amaranthus bioassay and for binding to the Arabidopsis cytokinin receptors AHK3 and AHK4.