Carboxylate-dependent gelation of a monoclonal antibody

Abstract

Purpose: This paper shows the first ever assembly of monoclonal antibody using multivalent carboxylate ions into highly ordered structures that feature viscoelastic properties reminiscent of other filamentous proteins.

Methods: A monoclonal antibody was assembled into filamentous networks by adding multivalent carboxylates to the protein solution. Gelation and characterization of these networks were monitored using mechanical rheometry, electron microscopy, Fourier transform infra-red and Raman spectroscopy.

Results: Electron microscopy and mechanical rheometry suggest the formation of rigid filament bundles that feature strong interfilament interactions. Filament network elasticity increased with multivalent carboxylate and protein concentrations, hinting at the importance of multivalent carboxylates in the mechanism of assembly.

Conclusion: Assembly is not triggered by high ionic strength but with multivalent carboxylates. A high protein concentration is required for filament formation and the elasticity of the networks are weakly dependent on concentration. The exact mechanism of assembly is still elusive, although we speculate that carboxylates could act as a bridge to crosslink antibody monomers. These monoclonal antibody monomers could be linked either through Fab-Fab or Fc-Fab regions, although previous reports have shown evidence of reversible self-association mediated through the Fab regions.