Journal
BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS
Volume 1698, Issue 2, Pages 213-218Publisher
ELSEVIER
DOI: 10.1016/j.bbapap.2003.12.002
Keywords
WGA; Trp fluorescence; TNS; cytokinin; abscisic acid; gibberellic acid
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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 muM). 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. (C) 2003 Elsevier B.V. All rights reserved.
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