Crystallization and preliminary X‐ray investigation of the recombinant Trypanosoma brucei rhodesiense calmodulin

Bipyramidal crystals of the recombinant calmodulin from Trypanosoma brucei rhodesiense were obtained by vapor diffusion against 55% (v/v) 2‐methyl‐2,4‐pentanediol in 0.05 M cacodylate buffer, pH 5.6. When few nucleation events occurred, crystals grew to 0.25 × 0.25 × 1.20 mm. The space group of the crystal is I 4 1 22, with unit cell dimensions a = b = 56.88 Å, c = 230.11 Å, α = β = γ = 90°, z = 16. The molecular mass and volume of the unit cell suggest that there is one molecule in the asymmetric unit. The I /σ( I ) ratio for data at 3.0 Å resolution was 3.67, indicating that the final structure can be refined at higher resolution. Molecular replacement methods and the PC‐refinement technique have not yet yielded the structure under a variety of search conditions. We are currently investigating the multiple isomorphous replacement approach to determine this crystal structure. © 1995 Wiley‐Liss, Inc.