title: Three-dimensional structure of gurmarin, a sweet taste-suppressing polypeptide.
abstract: The solution structure of gurmarin was studied by two-dimensional proton NMR spectroscopy at 600 MHz. Gurmarin, a 35-amino acid residue polypeptide recently discovered in an Indian-originated tree Gymnema sylvestre, selectively suppresses the neural responses of rat to sweet taste stimuli. Sequence-specific resonance assignments were obtained for all backbone protons and for most of the side-chain protons. The three-dimensional solution structure was determined by simulated-annealing calculations on the basis of 135 interproton distance constraints derived from NOEs, six distance constraints for three hydrogen bonds and 16 dihedral angle constraints derived from coupling constants. A total of 10 structures folded into a well-defined structure with a triple-stranded antiparallel beta-sheet. The average rmsd values between any two structures were 1.65 +/- 0.39 A for the backbone atoms (N, C alpha, C) and 2.95 +/- 0.27 A for all heavy atoms. The positions of the three disulfide bridges, which could not be determined chemically, were estimated to be Cys3-Cys18, Cys10-Cys23 and Cys17-Cys33 on the basis of the NMR distance constraints. This disulfide bridge pattern in gurmarin turned out to be analogous to that in omega-conotoxin and Momordica charantia trypsin inhibitor-II, and the topology of folding was the same as that in omega-conotoxin.
authors.affiliation: Department of Chemistry, Faculty of Science, Kyoto University, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Arai
authors.forename: R
authors.initials: R
authors.lastname: Ishima
authors.forename: S
authors.initials: S
authors.lastname: Morikawa
authors.forename: A
authors.initials: A
authors.lastname: Miyasaka
authors.forename: T
authors.initials: T
authors.lastname: Imoto
authors.forename: S
authors.initials: S
authors.lastname: Yoshimura
authors.forename: S
authors.initials: S
authors.lastname: Aimoto
authors.forename: K
authors.initials: K
authors.lastname: Akasaka
mesh_terms: D000595:Amino Acid Sequence; D003198:Computer Simulation; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry*; D010944:Plants / Q000737:chemistry; D017433:Protein Structure, Secondary; D014316:Tritium
chemical_list: D010940:Plant Proteins; D014316:Tritium; C075206:Gurmarin protein, Gymnema sylvestre