Structure of Designer Antibody-like Peptides Binding to the Human C5a with Potential to Modulate the C5a Receptor Signaling.

C5a is an integral glycoprotein of the complement system that plays an important role in inflammation and immunity. The physiological concentration of C5a is observed to be elevated under various immunoinflammatory pathophysiological conditions in humans. The pathophysiology of C5a is linked to the "two-site" protein-protein interactions (PPIs) with two genomically related receptors, such as C5aR1 and C5aR2. Therefore, pharmacophores that can potentially block the PPIs between C5a-C5aR1 and C5a-C5aR2 have tremendous potential for development as future therapeutics. Notably, the FDA has already approved antibodies that target the precursors of C5a (Eculizumab, 148 kDa) and C5a (Vilobelimab, 149 kDa) for marketing as complement-targeted therapeutics. In this context, the current study reports the structural characterization of a pair of synthetic designer antibody-like peptides (DePA and DePA1; ≤3.8 kDa) that bind to hotspot regions on C5a and also demonstrates potential traits to neutralize the function of C5a under pathophysiological conditions.