title: Structure of a Potential Therapeutic Antibody Bound to Interleukin-16 (IL-16): MECHANISTIC INSIGHTS AND NEW THERAPEUTIC OPPORTUNITIES.
abstract: Interleukin-16 (IL-16) is reported to be a chemoattractant cytokine and modulator of T-cell activation, and has been proposed as a ligand for the co-receptor CD4. The secreted active form of IL-16 has been detected at sites of TH1-mediated inflammation, such as those seen in autoimmune diseases, ischemic reperfusion injury (IRI), and tissue transplant rejection. Neutralization of IL-16 recruitment to its receptor, using an anti-IL16 antibody, has been shown to significantly attenuate inflammation and disease pathology in IRI, as well as in some autoimmune diseases. The 14.1 antibody is a monoclonal anti-IL-16 antibody, which when incubated with CD4(+) cells is reported to cause a reduction in the TH1-type inflammatory response. Secreted IL-16 contains a characteristic PDZ domain. PDZ domains are typically characterized by a defined globular structure, along with a peptide-binding site located in a groove between the αB and βB structural elements and a highly conserved carboxylate-binding loop. In contrast to other reported PDZ domains, the solution structure previously reported for IL-16 reveals a tryptophan residue obscuring the recognition groove. We have solved the structure of the 14.1Fab fragment in complex with IL-16, revealing that binding of the antibody requires a conformational change in the IL-16 PDZ domain. This involves the rotation of the αB-helix, accompanied movement of the peptide groove obscuring tryptophan residue, and consequent opening up of the binding site for interaction. Our study reveals a surprising mechanism of action for the antibody and identifies new opportunities for the development of IL-16-targeted therapeutics, including small molecules that mimic the interaction of the antibody.
authors.affiliation: From the Department of Molecular and Cell Biology, Henry Wellcome Building, University of Leicester, Leicester, LE1 9HN, United Kingdom, gh126@le.ac.uk.
authors.forename: Gareth
authors.initials: G
authors.lastname: Hall
authors.affiliation: MRC Technology, Centre for Therapeutics Discovery, 1-3 Burtonhole Lane, Mill Hill, London NW7 1AD, United Kingdom, and.
authors.forename: Eilish
authors.initials: E
authors.lastname: Cullen
authors.affiliation: MRC Technology, Centre for Therapeutics Discovery, 1-3 Burtonhole Lane, Mill Hill, London NW7 1AD, United Kingdom, and.
authors.forename: Kovilen
authors.initials: K
authors.lastname: Sawmynaden
authors.affiliation: MRC Technology, Centre for Therapeutics Discovery, 1-3 Burtonhole Lane, Mill Hill, London NW7 1AD, United Kingdom, and.
authors.forename: Joanne
authors.initials: J
authors.lastname: Arnold
authors.affiliation: MRC Technology, Centre for Therapeutics Discovery, 1-3 Burtonhole Lane, Mill Hill, London NW7 1AD, United Kingdom, and.
authors.forename: Simon
authors.initials: S
authors.lastname: Fox
authors.affiliation: From the Department of Molecular and Cell Biology, Henry Wellcome Building, University of Leicester, Leicester, LE1 9HN, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Cowan
authors.affiliation: From the Department of Molecular and Cell Biology, Henry Wellcome Building, University of Leicester, Leicester, LE1 9HN, United Kingdom.
authors.forename: Frederick W
authors.initials: FW
authors.lastname: Muskett
authors.affiliation: MRC Technology, Centre for Therapeutics Discovery, 1-3 Burtonhole Lane, Mill Hill, London NW7 1AD, United Kingdom, and david.matthews@tech.mrc.ac.uk.
authors.forename: David
authors.initials: D
authors.lastname: Matthews
authors.affiliation: MRC Technology, Centre for Therapeutics Discovery, 1-3 Burtonhole Lane, Mill Hill, London NW7 1AD, United Kingdom, and.
authors.forename: Andrew
authors.initials: A
authors.lastname: Merritt
authors.affiliation: MRC Technology, Centre for Therapeutics Discovery, 1-3 Burtonhole Lane, Mill Hill, London NW7 1AD, United Kingdom, and.
authors.forename: Catherine
authors.initials: C
authors.lastname: Kettleborough
authors.affiliation: the Boston University School of Medicine, Boston, Massachusetts 02118.
authors.forename: William
authors.initials: W
authors.lastname: Cruikshank
authors.affiliation: MRC Technology, Centre for Therapeutics Discovery, 1-3 Burtonhole Lane, Mill Hill, London NW7 1AD, United Kingdom, and.
authors.forename: Debra
authors.initials: D
authors.lastname: Taylor
authors.affiliation: From the Department of Molecular and Cell Biology, Henry Wellcome Building, University of Leicester, Leicester, LE1 9HN, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Bayliss
authors.affiliation: From the Department of Molecular and Cell Biology, Henry Wellcome Building, University of Leicester, Leicester, LE1 9HN, United Kingdom, mdc12@le.ac.uk.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Carr
mesh_terms: D000911:Antibodies, Monoclonal / Q000737:chemistry*; D001666:Binding Sites, Antibody; D018360:Crystallography, X-Ray; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry*; D019410:Interleukin-16 / Q000737:chemistry*; D000072417:Protein Domains; D017433:Protein Structure, Secondary
chemical_list: D000911:Antibodies, Monoclonal; D007140:Immunoglobulin Fab Fragments; D019410:Interleukin-16
keywords: cytokine; interleukin; interleukin-16; monoclonal antibody; nuclear magnetic resonance (NMR); protein crystallization