Structural and functional investigation of human chemokines and applications of human chemokines in blocking HIV-1 entry

Chemokines are important mediators of leukocyte migration. Chemokines bind to G protein–coupled receptors (GPCR) and cause conformational changes that trigger intracellular signaling pathways involved in inflammation, injury healing, cancer, metastasis, and HIV infections. No direct structural information about any chemokine receptor is available, but the structure of chemokines has been well studied. Structural studies of chemokines coupled with cell-biological investigations may lead to a better understanding of the mechanisms of chemokine-receptor interactions. In this Ph.D. project, I studied the structural and functional relationship between chemokines and chemokine receptors using NMR, X-ray crystallography, and mutagenesis approaches, coupled with several different cell-biology assays. We found that the conserved “chemokine fold” can support different dimerization types in the chemokines family, although changing the dimers from CC- to CXC-type fold is not readily accomplished. I also used an engineered covalently-bound dimer of the MIP-1β mutant, MIP-1β-A10C, to study the relationship between dimerization of chemokines and their interaction with the CCR5 receptor. My results suggest that MIP-1β dimer neither bind nor activate the CCR5 receptor. I also studied the biophysical properties of one N-terminal awkward mutant of P2-RANTES, which was originally selected by others from a phage display using CCR5-expressing cells. Although the NMR and X-ray crystal studies revealed that the wild type RANTES is a tight homodimer, analytical ultracentrifugation reveals that P2-RANTES is a monomer in solution, the 1.7 Å resolution X-ray crystal structure of P2-RANTES was found to be a packed tetramer. The mutated N-terminal residues play a very important role in the tetramerization in the X-ray crystal structure. Finally I used the HIV-1 env mediated cell-cell fusion assay to study the combination of chemokines or chemokine variants with anti-HIV peptides C37 or/and T-20. A surprisingly synergistic effect was found between P2-RANTES and C37 or T-20. This combination stratagem may lead to further useful drug combinations or drug delivery for more potent anti-HIV treatments