Crystal structure of yellow meal worm α-amylase at 1.64 Å resolution

Abstract

The three-dimensional structure of the α-amylase from Tenebrio molitor larvae (TMA) has been determined by molecular replacement techniques using diffraction data of a crystal of space group P2 12 12 1 ( a = 51.24 Å; b = 93.46 Å; c = 96.95 Å). The structure has been refined to a crystallographic R-factor of 17.7% for 58,219 independent reflections in the 7.0 to 1.64 Å resolution range, with root-mean-square deviations of 0.008 Å for bond lengths and 1.482° for bond angles. The final model comprises all 471 residues of TMA, 261 water molecules, one calcium cation and one chloride anion. The electron density confirms that the N-terminal glutamine residue has undergone a post-transitional modification resulting in a stable 5-oxo-proline residue. The X-ray structure of TMA provides the first three-dimensional model of an insect α-amylase. The monomeric enzyme exhibits an elongated shape approximately 75 Å × 46 Å × 40 Å and consists of three distinct domains, in line with models for α-amylases from microbial, plant and mammalian origin. However, the structure of TMA reflects in the substrate and inhibitor binding region a remarkable difference from mammalian α-amylases: the lack of a highly flexible, glycine-rich loop, which has been proposed to be involved in a “trap-release” mechanism of substrate hydrolysis by mammalian α-amylases. The structural differences between α-amylases of various origins might explain the specificity of inhibitors directed exclusively against insect α-amylases.