Two distinct functional sites of human interleukin 4 are identified by variants impaired in either receptor binding or receptor activation.
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)
Kruse
N
N
Theodor-Boveri-Institut für Biowissenschaften (Biozentrum) der Universität, Würzburg, Germany.
Shen
B J
BJ
Arnold
S
S
Tony
H P
HP
Müller
T
T
Sebald
W
W
D000595:Amino Acid Sequence; D001402:B-Lymphocytes / Q000276:immunology*; D001667:Binding, Competitive; D006801:Humans; D015847:Interleukin-4 / Q000737:chemistry*; D008213:Lymphocyte Activation; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D019948:Receptors, Interleukin-4; D011975:Receptors, Mitogen / Q000737:chemistry*; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D013601:T-Lymphocytes / Q000276:immunology*; D014407:Tumor Cells, Cultured
D019948:Receptors, Interleukin-4; D011975:Receptors, Mitogen; D015847:Interleukin-4