Determination of the complete three-dimensional structure of the α-amylase inhibitor tendamistat in aqueous solution by nuclear magnetic resonance and distance geometry

The complete three-dimensional structure of the α-amylase inhibitor Tendamistat in aqueous solution was determined by ¹H nuclear magnetic resonance and distance geometry calculations using the program DISMAN. Compared to an earlier, preliminary determination of the polypeptide backbone conformation, stereo-specific assignments were obtained for 41 of the 89 prochiral groups in the protein, and a much more extensive set of experimental constraints was collected, including 842 distance constraints from nuclear Overhauser effects and over 100 supplementary constraints from spin-spin coupling constants and the identification of intramolecular hydrogen bonds. The complete protein molecule, including the amino acid side-chains is characterized by a group of nine structures corresponding to the results of the nine DISMAN calculations with minimal residual error functions. The average of the pairwise minimal root-mean-square distances among these nine structures is 0.85 Å for the polypeptide backbone, and 1.52 Å for all the heavy atoms. The procedures used for the structure determination are described and a detailed analysis is presented of correlations between the experimental input data and the precision of the structure determination.