Targeting the fusion machinery of Peste des petits ruminants virus: design and in vitro characterization of an HRC-derived antiviral peptide.

Peste des petits ruminants virus (PPRV) is a highly contagious morbillivirus causing severe disease in small ruminants, with major implications for global food security and ongoing eradication efforts. Despite the availability of effective vaccines, the absence of antiviral therapeutics represents a critical gap in outbreak control. Here, we describe the design and in vitro characterization of a synthetic peptide derived from the heptad repeat C (HRC) region of the PPRV fusion (F) protein as a novel viral entry inhibitor. The HRC peptide potently inhibited PPRV F/H-mediated membrane fusion in a dose-dependent manner, with IC₅₀ values of 11.80 μM and 18.11 μM for SLAM/CD150- and nectin-4-dependent entry, respectively. Consistently, the peptide blocked viral entry in a vesicular stomatitis virus (VSV)-based pseudovirus system (IC₅₀ = 14.5 μM). Antiviral activity was further confirmed using a replicative morbillivirus model (canine distemper virus), where significant inhibition of infection was observed in both co-treatment and virus pre-treatment conditions. Notably, the combination with a fusion inhibitory compound (FIP) resulted in synergistic antiviral activity (FICI = 0.44), highlighting the potential of dual-targeting strategies. Biophysical analyses revealed a strong α-helical propensity in membrane-mimetic environments and high stability in human serum. Molecular docking and dynamics simulations indicated that the HRC peptide stabilizes the F protein by bridging critical domains through a persistent hydrogen-bond network, thereby preventing the conformational rearrangements required for membrane fusion. Collectively, these findings provide the first evidence that HRC-derived peptides can effectively inhibit PPRV entry and support their development as antiviral agents to complement current eradication strategies.