Fluorescence analysis of hormone binding activities of wheat germ agglutinin.
Wheat germ agglutinin (WGA) from embryos of the monocotyledonous plant Triticum vulgaris (Graminaceae) is a carbohydrate binding protein characterized by high specificity to N-acetyl-d-glucosamine and N-acetyl-d-neuraminic acid. In this study we show that parallel to its carbohydrate binding activities, WGA binds with several orders of magnitude higher affinity adenine, adenine-related cytokinins: kinetin, zeatin and isopentenyl-adenine as well as abscisic and gibberellic acids (K(d) 0.43-0.65 microM). Its interactions with these ligands cause conformational rearrangements in the protein molecules and significant enhancement of the protein tryptophan fluorescence (up to 60%) allowing characterization of the protein-hormone complexes. Dimeric WGA molecules possess two different classes of binding sites for the fluorescent hydrophobic probe 2-(p-toluidinyl) naphthalene sulfonic acid (TNS) as suggested by the sigmoid shape of the fluorescence titration curve and the value of the Hill coefficient (n(H) 1.6+/-0.3). The plant hormones displace part of the bound TNS probe and share the higher affinity TNS binding sites. These results characterize WGA as a hormone-binding protein.
Bogoeva
Vanya P
VP
Institute of Molecular Biology, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., B1.21, Sofia 1113, Bulgaria.
Radeva
Maya A
MA
Atanasova
Lyubomira Y
LY
Stoitsova
Stoyanka R
SR
Boteva
Raina N
RN
D000040:Abscisic Acid / Q000378:metabolism; D000225:Adenine / Q000378:metabolism; D003583:Cytokinins / Q000378:metabolism; D005875:Gibberellins / Q000378:metabolism; D006728:Hormones / Q000378:metabolism*; D009282:Naphthalenesulfonates; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D014909:Wheat Germ Agglutinins / Q000378:metabolism*
D003583:Cytokinins; D005875:Gibberellins; D006728:Hormones; D009282:Naphthalenesulfonates; D014909:Wheat Germ Agglutinins; D000040:Abscisic Acid; C009497:2-(4-toluidino)-6-naphthalenesulfonic acid; C007842:gibberellic acid; D000225:Adenine