title: Receptor-binding conformation of the "ELR" motif of IL-8: X-ray structure of the L5C/H33C variant at 2.35 A resolution.
abstract: The "ELR" (Glu-Leu-Arg) tripeptide sequence near the N-terminus of interleukin-8 (IL-8) contributes a large part of the receptor binding free energy. Prior X-ray and nuclear magnetic resonance (NMR) structures of IL-8 have shown this region of the molecule to be highly mobile. We reasoned that a hydrophobic interaction between the leucine and the neighboring beta-turn might exist in the receptor binding conformation of the N-terminus. To test this hypothesis, we mutated two residues to cysteine and connected the N-terminus to the beta-turn. The mutant retains receptor binding affinity reasonably close to wild type and allows the characterization of a high-affinity conformation that may be useful in the design of small IL-8 mimics. The L5C/H33C mutant is refined to R-values of R = 20.6% and Rfree = 27.7% at 2.35 A resolution. Other receptor binding determinants reside in the "N-loop" found after "ELR" and preceding the first beta-strand. All available structures of IL-8 have been found with one of two distinct N-loop conformations. One of these is relevant for receptor binding, based on NMR results with receptor peptides. The other conformation obscures the receptor-peptide binding surface and may have an undetermined but necessarily different function.
authors.affiliation: Department of Protein Engineering Genentech, Inc., South San Francisco, California, USA.
authors.forename: N
authors.initials: N
authors.lastname: Gerber
authors.forename: H
authors.initials: H
authors.lastname: Lowman
authors.forename: D R
authors.initials: DR
authors.lastname: Artis
authors.forename: C
authors.initials: C
authors.lastname: Eigenbrot
mesh_terms: D020816:Amino Acid Motifs; D019943:Amino Acid Substitution; D000818:Animals; D015703:Antigens, CD / Q000737:chemistry; D018360:Crystallography, X-Ray; D006801:Humans; D016209:Interleukin-8 / Q000737:chemistry* / Q000235:genetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011487:Protein Conformation; D018121:Receptors, Cytokine / Q000737:chemistry; D018123:Receptors, Interleukin / Q000737:chemistry; D023062:Receptors, Interleukin-8A
chemical_list: D015703:Antigens, CD; D016209:Interleukin-8; D018121:Receptors, Cytokine; D018123:Receptors, Interleukin; D023062:Receptors, Interleukin-8A