SOLUTION STRUCTURE AND BASIS FOR FUNCTIONAL-ACTIVITY OF STROMAL CELL-DERIVED FACTOR-I - DISSOCIATION OF CXCR4 ACTIVATION FROM BINDING AND INHIBITION OF HIV-1

The three-dimensional structure of stromal cell-derived factor-1 (SDF- 1) was determined by NMR spectroscopy, SDF-1 is a monomer with a disor dered N-terminal region (residues 1-8), and differs from other chemoki nes in the packing of the hydrophobic core and surface charge distribu tion, Results with analogs showed that the N-terminal eight residues f ormed an important receptor binding site; however, only Lys-1 and Pro- 2 were directly involved in receptor activation, Modification to Lys-1 and/or Pro-2 resulted in loss of activity, but generated potent SDF-1 antagonists, Residues 12-17 of the loop region, which we term the RFF ESH motif, unlike the N-terminal region, were well defined in the SDF- 1 structure, The RFFESH formed a receptor binding site, which we propo se to be an important initial docking site of SDF-1 with its receptor, The ability of the SDF-1 analogs to block HIV-1 entry via CXCR4, whic h is a HIV-1 coreceptor for the virus in addition to being the recepto r for SDF-1, correlated with their affinity for CXCR4, Activation of t he receptor is not required for HIV-1 inhibition.