Structure of the alpha-amylase inhibitor tendamistat at 0.93 A

The crystal structure of the proteinaceous alpha-amylase inhibitor tendamistat has been determined at 100 K to a resolution of 0.93 A. The final R factor for all reflections with F > 4sigma(F) is 9.26%. The mean coordinate error for fully occupied protein atoms as derived from full-matrix inversion is 0.018 A. An extended network of multiple discrete conformations has been identified on the side of tendamistat that binds to the target molecule. Most notably, residue Tyr15, which interacts with the glycine-rich loop characteristic of mammalian amylases, and a cluster of amino-acid side chains surrounding it are found in two well defined conformations. The flexibility observed in this crystal structure together with information about residues fixed by lattice contacts in the crystal but found to be mobile in a previous NMR study supports a model in which most of the residues involved in binding are not fixed in the free form of the inhibitor, suggesting an induced-fit type of binding.