1H NMR studies were carried out on interleukin 8 (IL-8) analogs in order to probe the structural features that are essential for receptor binding and function. The analogs studied were the chemically synthesized IL-8 (1–72), a series of N-terminally truncated derivatives (4–72, 5–72, and 6–72), and derivatives with single amino acid substitutions (I10A, R6K, and H33A). Previous functional studies have shown that the N-terminal residues, especially the residues at positions 4–6, and the β turn containing Cys-34, which is disulfide linked to Cys-7, are important for receptor affinity and functional activity [Clark-Lewis, I., Schumacher, C., Baggiolini, M., & Moser, B. (1991) J. Biol. Chem. 266, 23128–23134; Clark-Lewis, I., Dewald, B., Loetscher, M., Moser, B., & Baggiolini, M. (1994) J. Biol. Chem. (in press)]. The 6–72 and R6K analogs also showed properties of an antagonist. Analysis of the 1H NMR parameters such as chemical shifts, amide proton chemical shift temperature coefficients, and NOESY data indicates that the core structure is the same for all these proteins. Small differences were observed in some of the NMR properties for some of the residues in the N-terminal region and the turn containing Cys-34. Detailed analysis suggests that there is no correlation between these differences and observed function. Thus functional differences between the N-terminal analogs are a direct consequence of changes in receptor binding due to substitutions/ deletions in the N-terminal sequence and not due to structural changes elsewhere. NMR data for the H33A analog, which had the same activity as native IL-8, showed that the turn is essentially the same as in the native IL-8 and other analogs. Our data suggests that the protein core acts as a scaffold from which the N-terminal residues and the turn containing Cys-34 are suspended in the correct orientation to bind the receptor and elicit function.
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