Structure-Guided Design of C5aR1-Selective Peptide Agonists

Selective peptide agonists targeting complement C5a receptor 1 (C5aR1) are essential for studying receptor-specific inflammatory signaling, although their optimization is challenging due to similarities with related anaphylatoxin receptors and pathway-dependent pharmacology. In this study, a structure-guided computational workflow was employed to prioritize mutations within two C5a-derived peptide agonist scaffolds.

Using FoldX-guided modeling, position 5 was identified as a potential optimization site, with hydrophobic substitutions predicted to improve C5aR1 engagement without significant impact on C3aR binding. Predicted BM1 and BM221 analogues were synthesized via solid-phase peptide synthesis and evaluated for their effects on C3aR, C5aR1, and C5aR2 using ERK1/2 phosphorylation and β-arrestin recruitment assays.

Position-5 substitutions demonstrated enhanced functional preference for C5aR1 in ERK assays, although the replacement of Leu6 with Ala reduced target potency, indicating pathway-dependent receptor discrimination. The BM1 P5M substitution showed the greatest overall improvement across ERK and β-arrestin readouts. In the BM221 series, A5Nle substitution improved C5aR1 preference over C3aR, while A5Nle Abu6Ala produced the most favorable serum stability profile.

These findings suggest that position 5 is a transferable optimization site and emphasize the need to balance C5aR1 potency and receptor selectivity during the design of next-generation agonists.