title: Molecular characterization of CCR6: involvement of multiple domains in ligand binding and receptor signaling.
abstract: The CC chemokine receptor 6 (CCR6) is selectively expressed on memory T cells, B cells, and dendritic cells and appears to be involved in the initiation of a memory immune response. The only chemokine ligand for CCR6 is CCL20/MIP-3alpha. In the present study, we attempted to define the extracellular domains (ECDs) of CCR6 responsible for CCL20/MIP-3alpha binding using a domain-swapping approach in which the ECDs of CCR6 were substituted with the corresponding CCR5 domains to generate various CCR6/CCR5 chimeras. These chimeras were tested for receptor expression, ligand binding, and functional activity as evaluated by calcium flux and chemotaxis. All chimeras showed respectable surface expression; however only one, substituted with extracellular loop 1 from CCR5, showed reduced functional activity. The general failure of functionality of the CCR6/CCR5 chimeras may imply that characteristics of each ECD are critical for coordination among all the ECDs of CCR6. Additionally, of interest, a chimera containing all of the ECDs from CCR5 in the context of CCR6 neither responded to CCR5 ligands nor served as a coreceptor for macrophage-tropic HIV-1. These results suggest that not only ECDs but also transmembrane and intracellular domains of CCR5 are involved in both ligand binding and coreceptor activity.
authors.affiliation: Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan, ROC.
authors.forename: Li-Shaung
authors.initials: LS
authors.lastname: Ai
authors.forename: Sheau-Fen
authors.initials: SF
authors.lastname: Lee
authors.forename: Steve S L
authors.initials: SS
authors.lastname: Chen
authors.forename: Fang
authors.initials: F
authors.lastname: Liao
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015704:CD4 Antigens / Q000737:chemistry; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002633:Chemotaxis; D017931:DNA Primers / Q000737:chemistry; D003713:Dendritic Cells / Q000378:metabolism; D005434:Flow Cytometry; D015497:HIV-1 / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D019713:Receptors, CCR5 / Q000737:chemistry; D054399:Receptors, CCR6; D019707:Receptors, Chemokine / Q000737:chemistry* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
chemical_list: C106311:CCR6 protein, human; D015704:CD4 Antigens; D017931:DNA Primers; D008024:Ligands; D019713:Receptors, CCR5; D054399:Receptors, CCR6; D019707:Receptors, Chemokine; D011993:Recombinant Fusion Proteins; D002118:Calcium