Rational design of a receptor super-antagonist of human interleukin-6.
Interleukin-6 (IL-6) is a differentiation and growth factor for a variety of cell types and its excessive production plays a major role in the pathogenesis of multiple myeloma and post-menopausal osteoporosis. IL-6, a four-helix bundle cytokine, is believed to interact sequentially with two transmembrane receptors, the low-affinity IL-6 receptor (IL-6R alpha) and the signal transducer gp130, via distinct binding sites. In this paper we show that combined mutations in the predicted A and C helices, previously suggested to establish contacts with gp130, give rise to variants with no bioactivity but unimpaired binding to IL-6R alpha. These mutants behave as full and selective IL-6 receptor antagonists on a variety of human cell lines. Furthermore, a bifacial mutant was generated (called IL-6 super-antagonist) in which the antagonist mutations were combined with amino acid substitutions in the predicted D helix that increase binding for IL-6R alpha. The IL-6 super-antagonist has no bioactivity, but improved first receptor occupancy and, therefore, fully inhibits the wild-type cytokine at low dosage. The demonstration of functionally independent receptor binding sites on IL-6 suggests that it could be possible to design super-antagonists of other helical cytokines which drive the assembly of structurally related multisubunit receptor complexes.
Savino
R
R
Department of Genetics, Istituto di Ricerche di Biologia Molecolare (IRBM) P. Angeletti, Pomezia (Rome), Italy.
Ciapponi
L
L
Lahm
A
A
Demartis
A
A
Cabibbo
A
A
Toniatti
C
C
Delmastro
P
P
Altamura
S
S
Ciliberto
G
G
D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015195:Drug Design; D006801:Humans; D015850:Interleukin-6 / Q000031:analogs & derivatives* / Q000235:genetics / Q000494:pharmacology; D008113:Liver Neoplasms / Q000378:metabolism; D008958:Models, Molecular; D009101:Multiple Myeloma / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary; D018123:Receptors, Interleukin / Q000037:antagonists & inhibitors*; D019947:Receptors, Interleukin-6; D012680:Sensitivity and Specificity; D014407:Tumor Cells, Cultured
D015850:Interleukin-6; D018123:Receptors, Interleukin; D019947:Receptors, Interleukin-6