Structural and functional characterization of human CXCR4 as a chemokine receptor and HIV-1 co-receptor by mutagenesis and molecular modeling studies.
The human CXC chemokine receptor 4 (CXCR4) is a receptor for the chemokine stromal cell-derived factor (SDF-1alpha) and a co-receptor for the entry of specific strains of human immunodeficiency virus type I (HIV-1). CXCR4 is also recognized by an antagonistic chemokine, the viral macrophage inflammatory protein II (vMIP-II) encoded by human herpesvirus type VIII. SDF-1alpha or vMIP-II binding to CXCR4 can inhibit HIV-1 entry via this co-receptor. An approach combining protein structural modeling and site-directed mutagenesis was used to probe the structure-function relationship of CXCR4, and interactions with its ligands SDF-1alpha and vMIP-II and HIV-1 envelope protein gp120. Hypothetical three-dimensional structures were proposed by molecular modeling studies of the CXCR4.SDF-1alpha complex, which rationalize extensive biological information on the role of CXCR4 in its interactions with HIV-1 envelope protein gp120. With site-directed mutagenesis, we have identified that the amino acid residues Asp (D20A) and Tyr (Y21A) in the N-terminal domain and the residue Glu (E268A) in extracellular loop 3 (ECL3) are involved in ligand binding, whereas the mutation Y190A in extracellular loop 2 (ECL2) impairs the signaling mediated by SDF-1alpha. As an HIV-1 co-receptor, we found that the N-terminal domain, ECL2, and ECL3 of CXCR4 are involved in HIV-1 entry. These structural and mutational studies provide valuable information regarding the structural basis for CXCR4 activity in chemokine binding and HIV-1 viral entry, and could guide the design of novel targeted inhibitors.
Zhou
N
N
Kimmel Cancer Center, Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Luo
Z
Z
Luo
J
J
Liu
D
D
Hall
J W
JW
Pomerantz
R J
RJ
Huang
Z
Z
D001224:Aspartic Acid / Q000737:chemistry; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D018925:Chemokines / Q000737:chemistry*; D005434:Flow Cytometry; D017930:Genes, Reporter; D018698:Glutamic Acid / Q000737:chemistry; D015497:HIV-1 / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D019718:Receptors, CXCR4 / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D014443:Tyrosine / Q000737:chemistry
D018925:Chemokines; D008024:Ligands; D019718:Receptors, CXCR4; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D001224:Aspartic Acid; D018698:Glutamic Acid; D014443:Tyrosine; D002118:Calcium