Structural requirements for interleukin-8 function identified by design of analogs and CXC chemokine hybrids.
Structure-activity relationships of human interleukin-8 (IL-8) were probed using chemically synthesized analogs with single or double amino acid substitutions, as well as hybrids derived by substituting IL-8 regions into IP10, a related protein that lacks IL-8 activity. The analogs were tested for functional activity by measuring induction of elastase release from human neutrophils and competition for binding of radiolabeled IL-8. The hybrid studies indicated that Gly31 and Pro32, as well as the NH2-terminal region from IL-8 are required to convert IP10 into a fully functional protein, suggesting that these elements are critical for IL-8 activity. Both disulfide bridges, linking residue 7 to 34 and residue 9 to 50, were critical for function, as shown by substituting the cysteine pairs with alpha-aminobutyric acid. Single conservative substitutions were generally accepted into the 10-22 region of IL-8, which contrasts with the ELR motif (residues 4-6), previously shown to be essential for activity. The importance of residues within the 10-15 region and the 17-22 region was demonstrated with hybrids. In addition, some of the 4-22 residues have structural roles that may be important; for example, Tyr13, Phe17, and Phe21 are involved in aromatic interactions in the IL-8 structure, and are also moderately sensitive to modification. Except for Cys50, the results argue against a role for the 36-72 region, including the COOH-terminal alpha-helix, in receptor binding. We conclude that the disulfide bridges and 30-35 turn provide a structural scaffold for the NH2-terminal region which includes the primary receptor-binding site (the ELR motif) and secondary binding and conformational determinants between residues 10 and 22.
Clark-Lewis
I
I
Biomedical Research Centre, University of British Columbia, Vancouver, Canada.
Dewald
B
B
Loetscher
M
M
Moser
B
B
Baggiolini
M
M
D000595:Amino Acid Sequence; D054357:Chemokine CXCL10; D019743:Chemokines, CXC; D016207:Cytokines / Q000235:genetics; D006801:Humans; D016209:Interleukin-8 / Q000031:analogs & derivatives* / Q000235:genetics / Q000494:pharmacology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009504:Neutrophils / Q000187:drug effects*; D010196:Pancreatic Elastase / Q000378:metabolism; D018123:Receptors, Interleukin / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D013329:Structure-Activity Relationship
D054357:Chemokine CXCL10; D019743:Chemokines, CXC; D016207:Cytokines; D016209:Interleukin-8; D018123:Receptors, Interleukin; D011993:Recombinant Fusion Proteins; D010196:Pancreatic Elastase