Structure of thaumatin in a hexagonal space group: comparison of packing contacts in four crystal lattices.

The intensely sweet protein thaumatin has been crystallized in a hexagonal lattice after a temperature shift from 293 to 277 K. The structure of the protein in the new crystal was solved at 1.6 A resolution. The protein fold is identical to that found in three other crystal forms grown in the presence of crystallizing agents of differing chemical natures. The proportions of lattice interactions involving hydrogen bonds, hydrophobic or ionic groups differ greatly from one form to another. Moreover, the distribution of acidic and basic residues taking part in contacts also varies. The hexagonal packing is characterized by the presence of channels parallel to the c axis that are so wide that protein molecules can diffuse through them.