Three-dimensional structure of gurmarin, a sweet taste-suppressing polypeptide.
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.
Arai
K
K
Department of Chemistry, Faculty of Science, Kyoto University, Japan.
Ishima
R
R
Morikawa
S
S
Miyasaka
A
A
Imoto
T
T
Yoshimura
S
S
Aimoto
S
S
Akasaka
K
K
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
D010940:Plant Proteins; D014316:Tritium; C075206:Gurmarin protein, Gymnema sylvestre