Structure-function analysis of human IL-6 receptor: dissociation of amino acid residues required for IL-6-binding and for IL-6 signal transduction through gp130.
Here, we report the analysis of the structure-function relationship of the extracellular region of human interleukin 6 receptor (IL-6R). Upon binding of IL-6, IL-6R becomes associated extracellularly with a non-IL-6-binding but signal transducing molecule, gp130, and the IL-6 signal is generated. In this region, the cytokine receptor family domain, but not the immunoglobulin-like domain, was responsible both for IL-6 binding and for signal transduction through gp130. Because a soluble, extracellular portion of IL-6R (sIL-6R) could bind IL-6 and mediate IL-6 functions through gp130, amino acid substitutions were introduced into sIL-6R by site-directed mutagenesis. The results, together with the previously proposed tertiary structure model, suggested that the amino acid residues critical for IL-6 binding have a tendency to be distributed to the hinge region between the two 'barrel'-like fibronectin type III modules and to the same side of these two 'barrels'. Amino acid residues, of which substitutions barely affected the IL-6-binding but did abolish the IL-6 signalling capability of sIL-6R, were identified and found to be located mainly in the membrane proximal half of the second barrel. sIL-6R mutants carrying such substitutions lacked the capacity to associate with gp130 in the presence of IL-6.
Yawata
H
H
Division of Immunology, Osaka University, Japan.
Yasukawa
K
K
Natsuka
S
S
Murakami
M
M
Yamasaki
K
K
Hibi
M
M
Taga
T
T
Kishimoto
T
T
D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD; D002460:Cell Line; D002522:Chlorocebus aethiops; D050822:Cytokine Receptor gp130; D006023:Glycoproteins / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D015850:Interleukin-6 / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011971:Receptors, Immunologic / Q000737:chemistry* / Q000378:metabolism; D019947:Receptors, Interleukin-6; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D014162:Transfection
D015703:Antigens, CD; D006023:Glycoproteins; C494199:IL6ST protein, human; C494200:Il6st protein, mouse; D015850:Interleukin-6; D008562:Membrane Glycoproteins; D011971:Receptors, Immunologic; D019947:Receptors, Interleukin-6; D050822:Cytokine Receptor gp130