A chimeric MIP-1 alpha/RANTES protein demonstrates the use of different regions of the RANTES protein to bind and activate its receptors

Human RANTES (CCL5) and MIP-1 alpha (CCLS) bind rind activate several CC ch emokine receptors. RANTES is a high-affinity Ligand for CCR1 and CCR5, and it hinds CCR3 with moderate affinity and CCR4 with low affinity. MIP-1 alph a has similar binding characteristics to RANTES except that it does not bin d to CCR3. Here we have generated a chimera of human MIP-1 alpha. and RANTE S, called MIP/RANTES, consisting of the eight amino terminal residues of MI P-1 alpha preceding the CC motif, and the remainder of the sequence is RANT ES, The chimera is able to induce chemotaxis of human monocytes. MIP/RANTES has >100-fold reduction in binding to CCR1 and does not hind to CCR3 but r etains full, functional binding to CCR5, It has equivalent affinity for CCR 5 to MIP-1 alpha and RANTES, binding with an IC50 Of 1.12 nM, and is able t o mobilize calcium and induce endocytosis of CCR5 in PBMC in a manner equi- potent to RANTES, It also retains the ability to inhibit R5 using HIV-1 str ains. Therefore, we conclude that the amino terminus of RANTES is not invol ved in CCR5 binding, but it is essential for CCR1 and CCR3.