Plasmodium falciparum rab6 GTPase: expression, purification, crystallization and preliminary crystallographic studies

The Plasmodium falciparum rab6 gene encodes a 208 amino-acid polypeptide. Two recombinant versions of P. falciparum Rab6 protein were expressed in Escherichia coli: the full-length protein and a truncated form containing residues 1-175. Both forms were purified from the soluble fraction of bacterial extract and were purified by ion-exchange chromatography and size-exclusion chromatography. Purified proteins were crystallized at pH 6.5 using the hanging-drop vapor-diffusion technique at room temperature. The full-length protein diffracted to 2.4 A and belongs to the tetragonal space group P4(3)2(1)2 or P4(1)2(1)2, with unit-cell parameters a = b = 80. 6, c = 90.4 A. The crystals of the truncated protein were isomorphous with those of the full-length construct and diffracted X-rays to 2.2 A resolution.