Cryo-Electron Microscopy Structure of the ?IIb?3-Abciximab Complex.

ABSTRACT:

Objective

The ?IIb?3 antagonist antiplatelet drug abciximab is the chimeric antigen-binding fragment comprising the variable regions of murine monoclonal antibody 7E3 and the constant domains of human IgG1 and light chain ?. Previous mutagenesis studies suggested that abciximab binds to the ?3 C177-C184 specificity-determining loop (SDL) and Trp129 on the adjacent ?1-?1 helix. These studies could not, however, assess whether 7E3 or abciximab prevents fibrinogen binding by steric interference, disruption of either the ?IIb?3-binding pocket for fibrinogen or the ?3 SDL (which is not part of the binding pocket but affects fibrinogen binding), or some combination of these effects. To address this gap, we used cryo-electron microscopy to determine the structure of the ?IIb?3-abciximab complex at 2.8 Å resolution. Approach and Results: The interacting surface of abciximab is comprised of residues from all 3 complementarity-determining regions of both the light and heavy chains, with high representation of aromatic residues. Binding is primarily to the ?3 SDL and neighboring residues, the ?1-?1 helix, and ?3 residues Ser211, Val212 and Met335. Unexpectedly, the structure also indicated several interactions with ?IIb. As judged by the cryo-electron microscopy model, molecular-dynamics simulations, and mutagenesis, the binding of abciximab does not appear to rely on the interaction with the ?IIb residues and does not result in disruption of the fibrinogen-binding pocket; it does, however, compress and reduce the flexibility of the SDL.

Conclusions

We deduce that abciximab prevents ligand binding by steric interference, with a potential contribution via displacement of the SDL and limitation of the flexibility of the SDL residues.

SUBMITTER: Nesic D 

PROVIDER: S-EPMC7047619 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature