title: Structure-function relationship between the human chemokine receptor CXCR3 and its ligands.
abstract: I-TAC, IP10, and Mig are interferon-gamma inducible CXC chemokines that share the same G-protein-coupled receptor CXCR3, which is preferentially expressed on Th1 lymphocytes. We have explored the structure-function relationship of the CXCR3 ligands, in particular of I-TAC, which has highest affinity for CXCR3 and is the most potent agonist. A potent antagonist for CXCR3 was obtained by NH(2)-terminal truncation of I-TAC. I-TAC (4-73), which lacks the first three residues, has no agonistic activity but competes for the binding of I-TAC to CXCR3-bearing cells and inhibits migration and Ca(2+) changes in such cells in response to stimulation with I-TAC, IP10, and Mig. It does also not induce internalization of CXCR3, which is in support of the lack of agonistic effects. Hybrid chemokines between I-TAC and IP10 were used to identify regions responsible for the higher activity of I-TAC. I-TAC-like IP10 analogs are obtained by substituting the NH(2) terminus (residues 1-8) or N-loop region (residues 12-17) of IP10 with those of I-TAC, suggesting that the differences in function of the CXCR3 ligands can be assigned to distinct regions and that these regions are interchangeable. Structure-activity studies with Mig showed that the extended basic COOH-terminal region, which is not present in I-TAC and IP10, is important for binding and activity.
authors.affiliation: Biomedical Research Centre and Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada. ian@brc.ubc.ca
authors.forename: Ian
authors.initials: I
authors.lastname: Clark-Lewis
authors.forename: Ivan
authors.initials: I
authors.lastname: Mattioli
authors.forename: Jiang-Hong
authors.initials: JH
authors.lastname: Gong
authors.forename: Pius
authors.initials: P
authors.lastname: Loetscher
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D054357:Chemokine CXCL10; D054371:Chemokine CXCL11; D054370:Chemokine CXCL9; D019743:Chemokines, CXC / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002633:Chemotaxis / Q000502:physiology; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000378:metabolism; D008024:Ligands; D008969:Molecular Sequence Data; D011485:Protein Binding; D011869:Radioligand Assay; D054367:Receptors, CXCR3; D019707:Receptors, Chemokine / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment; D013329:Structure-Activity Relationship
chemical_list: C515202:CXCL11 protein, human; C080810:CXCL9 protein, human; C515187:CXCR3 protein, human; D054357:Chemokine CXCL10; D054371:Chemokine CXCL11; D054370:Chemokine CXCL9; D019743:Chemokines, CXC; D036341:Intercellular Signaling Peptides and Proteins; D008024:Ligands; D054367:Receptors, CXCR3; D019707:Receptors, Chemokine; D002118:Calcium