Identification of conformational core epitope Lys⁶⁸ in C5a based on the 3-D modeling complex C5a and its functional antibody F20

Abstract

Inhibition of C5a by antibodies has been demonstrated to dramatically improve survival in various sepsis models in mice and rats. The structural basis of C5a mediated bioactivity and C5a antibody mediated neutralization are of interesting to be investigated. In the previous study, we obtained a novel functional mouse antibody named as F20. With computer-guided modeling method, the 3-D theoretical structure of F20 Fv fragment was constructed. Using the crystal structure of C5a, the 3-D complex structure of C5a and F20 Fv fragment was modeled with molecular docking method. Based on distance geometry method and intermolecular interaction theory, the key residue Lys(68) in C5a identified by F20 was predicted. The mutant experimental results showed that the residue Lys(68) was the critical residue of C5a for it's bioactivity and F20 binding activity. The present study shed new light on the structural basis of C5a mediated bioactivity. The identification of the critical residue will provide useful information for human complement C5a targeted therapeutic intervention.