title: Asymmetric usage of antagonist charged residues drives interleukin-5 receptor recruitment but is insufficient for receptor activation.
abstract: The cyclic peptide AF17121 (VDECWRIIASHTWFCAEE) is a library-derived antagonist for human Interleukin-5 receptor alpha (IL5Ralpha). We have previously demonstrated that AF17121 mimics Interleukin-5 (IL5) by binding in a region of IL5Ralpha that overlaps the IL5 binding epitope. In the present study, to explore the functional importance of the amino acid residues of AF17121 required for effective binding to, and antagonism of, IL5Ralpha, each charged residue was subjected to site-directed mutagenesis and examined for IL5Ralpha interaction by using a surface plasmon resonance biosensor. One residue, Arg(6), was found to be essential for receptor antagonism; its replacement with either alanine or lysine completely abolished the interaction between AF17121 and IL5Ralpha. Other charged residues play modulatory roles. One class consists of the N-terminal acidic cluster (Asp(2) and Glu(3)) for which alanine replacement decreased the association rate. A second class consists of His(11) and the C-terminal acidic cluster (Glu(17) and Glu(18)) for which alanine replacement increased the dissociation rate. Binding model analysis of the mutants of the latter class of residues indicated the existence of conformational rearrangement during the interaction. On the basis of these results, we propose a model in which Arg(6) and N-terminal acidic residues drive the encounter complex, while Arg(6), His(11), and C-terminal acidic residues are involved in stabilizing the final complex. These data argue that the charged residues of AF17121 are utilized asymmetrically in the pathway of inhibitor-receptor complex formation to deactivate the receptor function. The results also help focus emerging models for the mechanism by which IL5 activates the IL5Ralpha-betac receptor system.
authors.affiliation: Department of Biochemistry and Molecular Biology and A. J. Drexel Institute of Basic and Applied Protein Science, Drexel University College of Medicine Pennsylvania 19102, USA.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ishino
authors.forename: Udaya
authors.initials: U
authors.lastname: Pillalamarri
authors.forename: Dominick
authors.initials: D
authors.lastname: Panarello
authors.forename: Madhushree
authors.initials: M
authors.lastname: Bhattacharya
authors.forename: Cecilia
authors.initials: C
authors.lastname: Urbina
authors.forename: Stephanie
authors.initials: S
authors.lastname: Horvat
authors.forename: Sanjay
authors.initials: S
authors.lastname: Sarkhel
authors.forename: Bradford
authors.initials: B
authors.lastname: Jameson
authors.forename: Irwin
authors.initials: I
authors.lastname: Chaiken
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001120:Arginine / Q000737:chemistry / Q000378:metabolism; D004330:Drosophila / Q000378:metabolism; D000939:Epitopes / Q000737:chemistry / Q000378:metabolism; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D053666:Interleukin-5 Receptor alpha Subunit; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010456:Peptides, Cyclic / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018123:Receptors, Interleukin / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D053649:Receptors, Interleukin-5; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship; D020349:Surface Plasmon Resonance; D013696:Temperature; D013879:Thioredoxins / Q000235:genetics / Q000378:metabolism
chemical_list: C509414:AF17121 peptide; D000939:Epitopes; C485918:IL5RA protein, human; D053666:Interleukin-5 Receptor alpha Subunit; D010456:Peptides, Cyclic; D018123:Receptors, Interleukin; D053649:Receptors, Interleukin-5; D011993:Recombinant Fusion Proteins; D006639:Histidine; D013879:Thioredoxins; D001120:Arginine