Analysis of the human interleukin-6/human interleukin-6 receptor Binding interface at the amino acid level : Proposed mechanism of interaction

• Published in: Blood 1997-02, Vol.89 (4), p.1319-1333
• Main Authors: KALAI, M, MONTERO-JULIAN, F. A, GRÖTZINGER, J, FONTAINE, V, VANDENBUSSCHE, P, DESCHUYTENEER, R, WOLLMER, A, BRAILLY, H, CONTENT, J
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Analysis of the immune response. Humoral and cellular immunity; Antibodies, Monoclonal - immunology; Antigens, CD - chemistry; Antigens, CD - genetics; Antigens, CD - metabolism; Binding Sites; Biological and medical sciences; Chemical Phenomena; Chemistry, Physical; Fundamental and applied biological sciences. Psychology; Fundamental immunology; Humans; Immunobiology; Interleukin-6 - chemistry; Interleukin-6 - genetics; Interleukin-6 - metabolism; Lymphokines, interleukins ( function, expression); Melanoma - pathology; Models, Molecular; Molecular Sequence Data; Mutagenesis, Site-Directed; Protein Binding; Protein Conformation; Receptors, Cell Surface - chemistry; Receptors, Interleukin - chemistry; Receptors, Interleukin - genetics; Receptors, Interleukin - metabolism; Receptors, Interleukin-6; Regulatory factors and their cellular receptors; Sequence Alignment; Sequence Homology, Amino Acid; Signal Transduction; Structure-Activity Relationship; Tumor Cells, Cultured
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.v89.4.1319

The interaction between interleukin-6 (IL-6) and IL-6 receptor (IL-6R) is the initial and most specific step in the IL-6 signaling pathway. Understanding its mechanism at the amino acid level is the basis for developing small IL-6-inhibiting molecules. We studied the human IL-6 (hIL-6)/hIL-6R binding interface by a combination of molecular modelling and site-directed mutagenesis. Our model suggests that the center of the interface between the two molecules consists of hydrophobic contacts predicted to account for most of the binding-free energy. These contacts can be regarded as a hydrophobic core shielded by hydrophilic residues that are also needed for recognition. Following this hypothesis, we altered in hIL-6 and hIL-6R residues predicted to reside in the contact region and to interact with each other. We studied the capacity of these mutants to form an IL-6/IL-6R complex and their ability to transduce the signal. This combined approach has led to the identification of certain residue-clusters in the binding interface and to a rational explanation of their specific interactions, suggesting therein a likely mechanism of complex formation. The results confirm the predictive model and strongly support our hypothesis. Comparison with other cytokines and their alpha-subunit receptors suggests that the structural location of certain binding sites are conserved.