In silico investigation of mAbs conformational changes upon antigen binding: impact of glycosylation and light chain isotype

Monoclonal antibodies (mAbs) represent a major class of biopharmaceuticals employed for the treatment of diseases such as cancer, asthma, and cardiovascular disorders. Glycosylation of mAbs, specifically occurring on the Fc region, affects their binding affinity to FcγRIIIa, with core fucosylation reducing the stability of the interaction. Additionally, the light chain (LC) isotype influences the conformational behavior of mAbs, modulating Fab rotation and Fc opening. In this study, we employed accelerated MD simulations to explore the impact of the antigen on the conformational dynamics of mAbs, focusing on how glycosylation patterns and LC isotype influence this process. Specifically, we examined two commercial antibodies differing in the LC composition, adalimumab and avelumab, in both G0 and G0F glycosylation states. Our results reveal that antigen binding induces conformational changes in the Fab and Fc regions, with glycosylation influencing the rearrangements in the Fc: G0 mAbs show an opening of the region, while G0F mAbs exhibit Fc closure. Furthermore, we observed that k-LC mAbs (adalimumab) display more extensive Fc rearrangements compared to λ-containing mAbs (avelumab), which show restricted Fc flexibility. These findings suggest that fucose and λ LC isotypes introduce structural constraints that may limit immune receptor interactions. Notably, antigen binding triggers an allosteric effect that affects distant Fc and hinge regions, whose rearrangement is crucial for the secondary mechanism of action of these molecules. Our study highlights the importance of antibody conformation in facilitating immune receptors engagement, suggesting that antigen binding in both adalimumab and avelumab enables conformational changes that might impact FcγRIIIa interaction and, therefore, antibody-dependent cellular cytotoxicity (ADCC).