title: Structural Mimicry of Receptor Interaction by Antagonistic Interleukin-6 (IL-6) Antibodies.
abstract: Interleukin 6 plays a key role in mediating inflammatory reactions in autoimmune diseases and cancer, where it is also involved in metastasis and tissue invasion. Neutralizing antibodies against IL-6 and its receptor have been approved for therapeutic intervention or are in advanced stages of clinical development. Here we describe the crystal structures of the complexes of IL-6 with two Fabs derived from conventional camelid antibodies that antagonize the interaction between the cytokine and its receptor. The x-ray structures of these complexes provide insights into the mechanism of neutralization by the two antibodies and explain the very high potency of one of the antibodies. It effectively competes for binding to the cytokine with IL-6 receptor (IL-6R) by using side chains of two CDR residues filling the site I cavities of IL-6, thus mimicking the interactions of Phe(229) and Phe(279) of IL-6R. In the first antibody, a HCDR3 tryptophan binds similarly to hot spot residue Phe(279) Mutation of this HCDR3 Trp residue into any other residue except Tyr or Phe significantly weakens binding of the antibody to IL-6, as was also observed for IL-6R mutants of Phe(279) In the second antibody, the side chain of HCDR3 valine ties into site I like IL-6R Phe(279), whereas a LCDR1 tyrosine side chain occupies a second cavity within site I and mimics the interactions of IL-6R Phe(229).
authors.affiliation: From argenx, 9052 Zwijnaarde, Belgium.
authors.forename: Christophe
authors.initials: C
authors.lastname: Blanchetot
authors.affiliation: From argenx, 9052 Zwijnaarde, Belgium.
authors.forename: Natalie
authors.initials: N
authors.lastname: De Jonge
authors.affiliation: Architecture et Fonction des Macromolécules Biologiques, UMR 6098 CNRS and Universités of Marseille, 13284 Marseille, France.
authors.forename: Aline
authors.initials: A
authors.lastname: Desmyter
authors.affiliation: From argenx, 9052 Zwijnaarde, Belgium.
authors.forename: Nico
authors.initials: N
authors.lastname: Ongenae
authors.affiliation: From argenx, 9052 Zwijnaarde, Belgium.
authors.forename: Erik
authors.initials: E
authors.lastname: Hofman
authors.affiliation: From argenx, 9052 Zwijnaarde, Belgium.
authors.forename: Alex
authors.initials: A
authors.lastname: Klarenbeek
authors.affiliation: From argenx, 9052 Zwijnaarde, Belgium.
authors.forename: Ava
authors.initials: A
authors.lastname: Sadi
authors.affiliation: From argenx, 9052 Zwijnaarde, Belgium.
authors.forename: Anna
authors.initials: A
authors.lastname: Hultberg
authors.affiliation: Bird Rock Bio, La Jolla, California 92037.
authors.forename: Anke
authors.initials: A
authors.lastname: Kretz-Rommel
authors.affiliation: Architecture et Fonction des Macromolécules Biologiques, UMR 6098 CNRS and Universités of Marseille, 13284 Marseille, France.
authors.forename: Silvia
authors.initials: S
authors.lastname: Spinelli
authors.affiliation: Structural Biology Brussels, Vrije Universiteit Brussel, 1050 Brussels, Belgium, and the Structural Biology Research Center, Instituut voor Biotechnologie, 1050 Brussels, Belgium.
authors.forename: Remy
authors.initials: R
authors.lastname: Loris
authors.affiliation: Architecture et Fonction des Macromolécules Biologiques, UMR 6098 CNRS and Universités of Marseille, 13284 Marseille, France.
authors.forename: Christian
authors.initials: C
authors.lastname: Cambillau
authors.affiliation: From argenx, 9052 Zwijnaarde, Belgium, hdehaard@argenx.com.
authors.forename: Hans
authors.initials: H
authors.lastname: de Haard
mesh_terms: D000818:Animals; D002162:Camelus; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry* / Q000276:immunology*; D015850:Interleukin-6 / Q000737:chemistry / Q000276:immunology; D051379:Mice; D020836:Protein Structure, Quaternary; D019947:Receptors, Interleukin-6 / Q000737:chemistry* / Q000276:immunology*; D000093242:Interleukin-6 Inhibitors
chemical_list: D007140:Immunoglobulin Fab Fragments; D015850:Interleukin-6; D019947:Receptors, Interleukin-6; D000093242:Interleukin-6 Inhibitors; C508600:IL6 protein, human
keywords: antibody engineering; crystal structure; high affinity; immunology; interleukin 6 (IL-6); structure-function