Structure determination of a small protein through a 23-dimensional molecular-replacement search.

The crystal structure of a 4-alpha-helical bundle protein has been determined by the application of a 23-dimensional molecular-replacement search performed using a stochastic method. The search model for the calculation was a 26-residue-long polyalanine helix amounting to less than 13% of the total number of atoms in the asymmetric unit of the target crystal structure. The crystal structure determination procedure is presented in detail, with emphasis on the molecular-replacement calculations.