Structures of CRP antigen-antibody complexes provide insights into the mechanism of specific recognition.

Antigen-antibody specific recognition constitutes fundamental research in molecular drug design and immune diagnostics, where cumulative non-covalent interactions critically determine binding affinities. Current mechanistic understanding of antibody affinity optimization remains incomplete, hindering rational structure-based design of therapeutic antibodies and bispecific variants. This study presents four cryo-EM structures of C-reactive protein (CRP) complexed with heavy-chain antibodies (HCAbs) of varying affinities, resolved at 3.0-3.4 Å resolution. Comparative structural analysis reveals pronounced variations in binding modalities among affinity-differentiated HCAbs, while identifying critical determinants of engagement conformations, providing mechanistic insights for rational optimization of CRP-specific antibodies.