The cytosolic fraction of Vigna radiata contains a 17-kD protein that binds plant hormones from the cytokinin group, such as zeatin. Using recombinant protein and isothermal titration calorimetry as well as fluorescence measurements coupled with ligand displacement, we have reexamined the K(d) values and show them to range from approximately 10(-6) M (for 4PU30) to 10(-4) M (for zeatin) for 1:1 stoichiometry complexes ...
The cytosolic fraction of Vigna radiata contains a 17-kD protein that binds plant hormones from the cytokinin group, such as zeatin. Using recombinant protein and isothermal titration calorimetry as well as fluorescence measurements coupled with ligand displacement, we have reexamined the K(d) values and show them to range from approximately 10(-6) M (for 4PU30) to 10(-4) M (for zeatin) for 1:1 stoichiometry complexes. In addition, we have crystallized this cytokinin-specific binding protein (Vr CSBP) in complex with zeatin and refined the structure to 1.2 A resolution. Structurally, Vr CSBP is similar to plant pathogenesis-related class 10 (PR-10) proteins, despite low sequence identity (<20%). This unusual fold conservation reinforces the notion that classic PR-10 proteins have evolved to bind small-molecule ligands. The fold consists of an antiparallel beta-sheet wrapped around a C-terminal alpha-helix, with two short alpha-helices closing a cavity formed within the protein core. In each of the four independent CSBP molecules, there is a zeatin ligand located deep in the cavity with conserved conformation and protein-ligand interactions. In three cases, an additional zeatin molecule is found in variable orientation but with excellent definition in electron density, which plugs the entrance to the binding pocket, sealing the inner molecule from contact with bulk solvent.
Related Citations:
Crystallization and preliminary crystallographic studies of mung bean cytokinin-specific binding protein Bujacz, G., Pasternak, O., Fujimoto, Y., Hashimoto, Y., Sikorski, M.M., Jaskolski, M. (2003) Acta Crystallogr D Biol Crystallogr 59: 522
Purification and cDNA cloning of cytokinin-specific binding protein from mung bean (Vigna radiata) Fujimoto, Y., Nagata, R., Fukasawa, H., Yano, K., Azuma, M., Iida, A., Sugimoto, S., Shudo, K., Hashimoto, Y. (1998) Eur J Biochem 258: 794
Crystal structures of two homologous pathogenesis-related proteins from yellow lupine Biesiadka, J., Bujacz, G., Sikorski, M.M., Jaskolski, M. (2002) J Mol Biol 319: 1223
Structure of a yellow lupine pathogenesis-related PR-10 protein belonging to a novel subclass Pasternak, O., Biesiadka, J., Dolot, R., Handschuh, L., Bujacz, G., Sikorski, M.M., Jaskolski, M. (2005) Acta Crystallogr D Biol Crystallogr 61: 99
X-ray and NMR structure of Bet v 1, the origin of birch pollen allergy. Gajhede, M., Osmark, P., Poulsen, F.M., Ipsen, H., Larsen, J.N., van Neerven, R.J.J., Schou, C., Lowenstein, H., Spangford, M.D. (1996) Nat Struct Biol 3: 1040
Organizational Affiliation:
Institute of Bioorganic Chemistry, Polish Academy of Sciences, 61704 Poznan, Poland.
Download Mendeley
