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Evidence for negative binding cooperativity within CCR5-CCR2b heterodimers
Laïla El-Asmar1, Jean-Yves Springael, Sébastien Ballet
1Institut de Recherche Interdisciplinaire en Biologie Humaine et Moléculaire, ULB campus Erasme, 808 route de Lennik, B-1070 Brussels, Belgium.
Molecular Pharmacology
|October 29, 2004
Summary
Chemokine receptors CCR5 and CCR2b form homo- and heterodimers efficiently. Ligand binding studies reveal that a receptor dimer binds only one chemokine, impacting inflammatory disease and HIV research.
Area of Science:
- Cellular and Molecular Biology
- Immunology
- Virology
Background:
- G protein-coupled receptors (GPCRs) form homo- and heterodimers, but functional outcomes are often unclear.
- Chemokine receptor CCR5 is crucial in inflammatory diseases and serves as an HIV coreceptor.
- CCR5 is known to homodimerize and heterodimerize with CCR2b.
Purpose of the Study:
- To investigate the functional consequences of CCR5 and CCR2b dimerization.
- To analyze effects on ligand binding, intracellular signaling, and receptor internalization.
Main Methods:
- Bioluminescence resonance energy transfer (BRET) assays.
- Coimmunoprecipitation assays.
- Fluorescence-activated cell sorting (FACS) analysis.
- Ligand binding and internalization assays.
Main Results:
- CCR5 and CCR2b heterodimerize with similar efficiency to homodimerization.
- No cooperative signaling observed upon costimulation with respective ligands.
- CCR5 ligands cross-competed for MCP-1 binding on coexpressed receptors.
- MCP-1 (CCR2b ligand) cross-competed for MIP-1beta binding on coexpressed receptors.
- Cointernalization was not observed upon agonist stimulation.
Conclusions:
- CCR5 and CCR2b form homo- and heterodimers with comparable efficiencies.
- A single chemokine binds to a receptor dimer, explaining cross-competition effects.
- Findings contribute to understanding chemokine receptor function in inflammation and HIV