Engineering C1q single-chain globular head variants for enhanced IgM binding

Expression levels differed among the globular head C1q variants, and SDS-PAGE analysis revealed variations in migration mobility, suggesting conformational differences. Four variants showed enhanced IgM binding compared to the wild type variant indicated by improved C1q displacement in the competitive interaction assay. These results were further supported by an advanced complement activation assay, where these variants significantly inhibited complement activation. These findings underpin the critical role of specific amino acids for IgM/C1q interaction and highlight the potential of engineered C1q as a potent inhibitor or activator of the classical complement cascade.