Crystallization of Clonorchis sinensis 26 kDa glutathione S-transferase and its fusion proteins with peptides of different lengths

A Clonorchis sinensis 26 kDa glutathione S-transferase (CsGST) and its fusion proteins containing 14 and 48 amino-acid peptides at the N-­terminus have been crystallized using polyethylene glycol monomethylether 550 as a precipitant. Crystals of the three proteins show very similar crystal properties: they diffract to at least 2.3 Å resolution and belong to the orthorhombic space group P2₁2₁2₁. The unit-cell parameters of CsGST crystals were a = 66.64 (1), b = 68.91 (1), c = 123.41 (2) Å, which are very close to those of the crystals of the two fusion proteins. In addition, CsGST fusion proteins containing varying extents of N-terminal-extended peptides are incorporated into a crystal, indicating that the extended peptides have little effect on crystal packing. These results suggest that the crystallization system of CsGST/peptide fusion protein may be generally applicable to obtain crystals of small peptides.