Human CCL5 trimer: expression, purification and initial crystallographic studies.

The chemokine CCL5 is considered to be a potential therapeutic target because of its ability to recruit immune cells to inflammatory sites. CCL5 aggregates under physiological conditions, and high-order oligomer formation is considered to be significant for cell migration, immune-cell activation and HIV cell entry. The structure of the high-order oligomer is unknown and the mechanism by which the oligomer is derived has yet to be established. Here, a CCL5 mutant (CCL5-E66S) which is deficient in oligomer formation was mixed with native CCL5 to prepare a protein trimer. At an optimized ratio the trimeric CCL5 crystallized, and the crystal belonged to the tetragonal space group P422, with unit-cell parameters a = 56.6, b = 56.6, c = 154.1 Å. The Matthews coefficient (V) of the crystal is 2.58 Å Da (three molecules in the asymmetric unit), with a solvent content of 52.32%. Diffraction data were collected to a resolution of 1.87 Å and the statistics indicated satisfactory data quality. The new structure will reveal the interfaces in the CCL5 oligomer, therefore assisting in understanding the mechanism of CCL5 oligomerization.