Two distinct functional sites of human interleukin 4 are identified by variants impaired in either receptor binding or receptor activation

EMBO J. 1993 Dec 15;12(13):5121-9.

Abstract

Interleukin 4 (IL-4) exerts a decisive role in the coordination of protective immune responses against parasites, particularly helminths. A disregulation of IL-4 function is possibly involved in the genesis of allergic disease states. The search for important amino acid residues in human IL-4 by mutational analysis of charged invariant amino acid positions identified two distinct functional sites in the 4-helix-bundle protein. Site 1 was marked by amino acid substitutions of the glutamic acid at position 9 in helix A and arginine at position 88 in helix C. Exchanges at both positions led to IL-4 variants deficient in binding to the extracellular domain of the IL-4 receptor (IL-4R(ex)). In parallel, up to 1000-fold increased concentrations of this type of variant were required to induce T-cell proliferation and B-cell CD23 expression. Site 2 was marked by amino acid exchanges in helix D at positions 121, 124 and 125 (arginine, tyrosine and serine respectively in the wild-type). IL-4 variants affected at site 2 exhibited partial agonist activity during T-cell proliferation; however, they still bound with high affinity to IL-4R(ex). [The generation of an IL-4 antagonist by replacing tyrosine 124 with aspartic acid has been described before by Kruse et al. (1992) (EMBO J., 11, 3237-3244)]. These findings indicate that IL-4 functions by binding IL-4R(ex) via site 1 which is constituted by residues on helices A and C.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • B-Lymphocytes / immunology*
  • Binding, Competitive
  • Humans
  • Interleukin-4 / chemistry*
  • Lymphocyte Activation*
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Protein Binding
  • Protein Structure, Tertiary
  • Receptors, Interleukin-4
  • Receptors, Mitogen / chemistry*
  • Signal Transduction
  • Structure-Activity Relationship
  • T-Lymphocytes / immunology*
  • Tumor Cells, Cultured

Substances

  • Receptors, Interleukin-4
  • Receptors, Mitogen
  • Interleukin-4