A NOVEL CYTOKININ-BINDING PROPERTY OF MISTLETOE LECTIN I FROM VISCUM ALBUM

Lectins are proteins known for their ability to recognize and bind specific carbohydrates. In addition to their carbohydrate-binding sites, some lectins possess hydrophobic sites and binding pockets capable of accommodating ligands such as phytohormones. Using the fluorescence spectroscopy method, we studied the interaction of mistletoe lectin I (ML-I, from Viscum album) with hormones from the cytokinin group such as N-6-isopentenyladenine, zeatin, kinetin, and N-6-benzylaminopurine. Our results demonstrated that ML-I binds to the studied cytokinins with high affinity (Kd = 0.7-1.7 mu M). The interaction of NIL-I with the phytohormones causes conformational rearrangements within the protein and significant fluorescence increase (up to 40 %) upon ligand binding. The hyperbolic titration curves as well as the comparable binding affinities indicate that the cytokinins could accommodate the same binding site. This is the first spectroscopic study demonstrating the novel property of mistletoe lectin to bind several cytokinins. Due to the high affinity to phytohormones, ML-I could be related to the group of phytohormone-(cytokinin)-binding proteins. Biotechnol. & Biotechnol. Eq. 2013, 27(1), 3583-3585