Open AccessA mixed-charge pair in human interleukin 4 dominates high-affinity interaction with the receptor α chain
Author(s) -
Yonghong Wang,
Bo Shen,
Walter Sebald
Publication year - 1997
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.94.5.1657
Subject(s) - alanine , chemistry , side chain , helix (gastropod) , epitope , receptor , amino acid , stereochemistry , biology , biochemistry , antibody , genetics , ecology , organic chemistry , snail , polymer
Human interleukin 4 (IL-4) binds to its cellular receptor with aK d in the subnanomolar range, similar to many other 4-helix-bundle proteins interacting with members of the hematopoietin (cytokine) receptor superfamily. In the IL-4 system this interaction is predominantly determined by the extracellular domain (IL4-BP) of the receptor α chain (K d ≈ 150 pM). Now a high-resolution mutational and kinetic analysis has revealed that the high-affinity binding of IL-4 originates from a continuous patch of a few mostly polar or charged amino acid side chains located on helices A and C. The binding epitope comprises (i ) a set of side chains determining the dissociation rate (k off ) and (ii ) a partially overlapping set determining the association rate constant (k on ) of the IL-4/IL4-BP complex. Thek off epitope is assembled from two juxtaposed main determinants (Glu-9 and Arg-88) surrounded by five side chains (Ile-5, Thr-13, Arg-53, Asn-89, and Trp-91) of lower importance. The cumulative increase ink off after alanine substitution is 105 -fold for the central mixed-charge pair and 3 × 103 -fold for the satellites. Thek on epitope is formed by five positively charged residues on helix C (Lys-77, Arg-81, Lys-84, Arg-85, and Arg-88) and two neighboring residues on helix A (Glu-9 and Thr-13). The cumulative loss ink on of the alanine variants is only about 10-fold. These results provide the basis for an understanding of molecular recognition in cytokine receptor complexes and for an IL-4 antagonist design.