Biochemical and biophysical characterization of natural polyreactivity in antibodies

To become specialized binders, antibodies undergo a process called affinity maturation to maximize their binding affinity. Despite this process, some antibodies retain low-affinity binding to diverse epitopes in a phe-nomenon called polyreactivity. Here we seek to understand the molecular basis of this polyreactivity in an-tibodies. Our results highlight that polyreactive antigen-binding fragments (Fabs) bind their targets with low affinities, comparable to T cell receptor recognition of autologous classical major histocompatibility com-plex. Extensive mutagenic studies find no singular amino acid residue or biochemical property responsible for polyreactive interaction, suggesting that polyreactive antibodies use multiple strategies for engagement. Finally, our crystal structures and all-atom molecular dynamics simulations of polyreactive Fabs show increased rigidity compared to their monoreactive relatives, forming a neutral and accessible platform for diverse antigens to bind. Together, these data support a cooperative strategy of rigid neutrality in establish-ing the polyreactive status of an antibody molecule.

Automated summary

This study investigates the molecular basis of polyreactivity in antibodies. It is found that polyreactive antigen-binding fragments (Fabs) bind their targets with low affinities, comparable to T cell receptor recognition. Mutagenic studies suggest that polyreactive antibodies use multiple strategies for engagement. The crystal structures and molecular dynamics simulations reveal increased rigidity in polyreactive Fabs, providing a neutral and accessible platform for diverse antigens to bind.