title: Substitutions in a homologous region of extracellular loop 2 of CXCR4 and CCR5 alter coreceptor activities for HIV-1 membrane fusion and virus entry.
abstract: CXCR4 and CCR5 are the principal coreceptors for human immunodeficiency virus type-1 (HIV-1) infection. Previously, mutagenesis of CXCR4 identified single amino acid changes that either impaired CXCR4's coreceptor activity for CXCR4-dependent (X4) isolate envelope glycoproteins (Env) or expanded its activity, allowing it to serve as a functional coreceptor for CCR5-dependent (R5) isolates. The most potent of these point mutations was an alanine substitution for the aspartic acid residue at position 187 in extracellular loop 2 (ecl-2), and here we show that this mutation also permits a variety of primary R5 isolate Envs, including those of other subtypes (clades), to employ it as a coreceptor. We also examined the corresponding region of CCR5 and demonstrate that the substitution of the serine residue in the homologous ecl-2 position with aspartic acid impairs CCR5 coreceptor activity for isolates across several clades. These results highlight a homologous and critical element in ecl-2, of both the CXCR4 and CCR5 molecules, for their respective coreceptor activities. Charge elimination expands CXCR4 coreceptor activity, while a similar charge introduction can destroy the coreceptor function of CCR5. These findings provide further evidence that there are conserved elements in both CXCR4 and CCR5 involved in coreceptor function.
authors.affiliation: Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Chabot
authors.forename: C C
authors.initials: CC
authors.lastname: Broder
mesh_terms: D000595:Amino Acid Sequence; D002459:Cell Fusion; D015686:Gene Products, env / Q000378:metabolism*; D015497:HIV-1 / Q000378:metabolism*; D008561:Membrane Fusion; D008969:Molecular Sequence Data; D017354:Point Mutation; D019713:Receptors, CCR5 / Q000235:genetics / Q000378:metabolism*; D019718:Receptors, CXCR4 / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014760:Viral Fusion Proteins / Q000378:metabolism*
chemical_list: D015686:Gene Products, env; D019713:Receptors, CCR5; D019718:Receptors, CXCR4; D014760:Viral Fusion Proteins