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 P4₁2₁2, with unit-cell parameters a = 56.6, b = 56.6, c = 154.1 Å. The Matthews coefficient (V_M) of the crystal is 2.58 ų Da^-1 (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.In order to study the oligomeric structure of human CCL5, a new strategy to prepare the CCL5 trimer was developed and a crystal was obtained that diffracted to a satisfactory resolution of 1.87 Å.