Abstract
Monoclonal antibodies against TNFα, including infliximab, adalimumab, golimumab, and certolizumab pegol, are widely used for the treatment of the inflammatory diseases such as rheumatoid arthritis and inflammatory bowel disease. Recently, the crystal structures of TNFα, in complex with the Fab fragments of infliximab and adalimumab, have revealed the molecular mechanisms of these antibody drugs. Here, we report the crystal structure of TNFα in complex with the Fab fragment of certolizumab pegol to clarify the precise antigen-antibody interactions and the structural basis for the neutralization of TNFα by this therapeutic antibody. The structural analysis and the mutagenesis study revealed that the epitope is limited to a single protomer of the TNFα trimer. Additionally, the DE loop and the GH loop of TNFα play critical roles in the interaction with certolizumab, suggesting that this drug exerts its effects by partially occupying the receptor binding site of TNFα. In addition, a conformational change of the DE loop was induced by certolizumab binding, thereby interrupting the TNFα-receptor interaction. A comprehensive comparison of the interactions of TNFα blockers with TNFα revealed the epitope diversity on the surface of TNFα, providing a better understanding of the molecular mechanism of TNFα blockers. The accumulation of these structural studies can provide a basis for the improvement of therapeutic antibodies against TNFα.
Highlights
Tumor necrosis factor superfamily (TNFSF) proteins mediate a diverse range of signaling events, including cell growth, survival, and apoptosis, and modulate inflammation, host defense, and organogenesis of the immune, ectodermal, and nervous systems [1,2,3]
We examined the binding mode of the complex and the conformational changes induced by antibody binding, thereby clarifying the molecular basis by which certolizumab pegol effectively blocks TNFα-TNFR interactions, despite the monovalency originating from its unique structure
Five biological agents against TNFα have been approved by the Food and Drug Administration (FDA) including three monoclonal anti-TNFα full IgG1 antibodies, infliximab, adalimumab, and golimumab; the PEGylated Fab fragment of the anti-TNFα antibody certolizumab pegol; and the extracellular domain of the TNFR2/IgG1-Fc fusion protein etanercept (Table 2)
Summary
Tumor necrosis factor superfamily (TNFSF) proteins mediate a diverse range of signaling events, including cell growth, survival, and apoptosis, and modulate inflammation, host defense, and organogenesis of the immune, ectodermal, and nervous systems [1,2,3]. The binding of TNFSF proteins to their receptors (TNFRSF) initiates many pro-inflammatory immune responses. It has been known that there are more than 35 specific ligand-receptor pairs between TNFSF and TNFRSF [4]. TNFα is a trimeric transmembrane protein; it can be cleaved to release a soluble trimer [8,9]. Both a mature form of soluble TNFα as well as a precursor form of transmembrane TNFα can mediate various inflammatory responses [10,11]. Each protomer of a TNFα trimer is formed by a sandwich of an inner and outer β-sheet with all 10 strands [12]
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