Substitutions in a Homologous Region of Extracellular Loop 2 of CXCR4 and CCR5 Alter Coreceptor Activities for HIV-1 Membrane Fusion and Virus Entry

• Published in: The Journal of biological chemistry 2000-08, Vol.275 (31), p.23774-23782
• Main Authors: Chabot, Donald J., Broder, Christopher C.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; CCR5 protein; Cell Fusion; CXCR4 protein; Env protein; Gene Products, env - metabolism; HIV-1 - metabolism; Human immunodeficiency virus 1; Membrane Fusion; Molecular Sequence Data; Point Mutation; Receptors, CCR5 - genetics; Receptors, CCR5 - metabolism; Receptors, CXCR4 - genetics; Receptors, CXCR4 - metabolism; Sequence Homology, Amino Acid; Viral Fusion Proteins - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M003438200

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.