Targeting the membrane fusion event of human respiratory syncytial virus with rationally designed α-helical hairpin traps.

Aims: Rational design of protein scaffolds with specific biological functions/activities has attracted much attention over the past decades. In the present study, we systematically examine the trimer-of-hairpins (TOH) motif of human respiratory syncytial virus (RSV) F protein, which plays a central role in viral membrane fusion and is a coiled-coil six-helix bundle formed by the antiparallel intermolecular interaction between three N-terminal heptad-repeat (HRN) helices and three C-terminal heptad-repeat (HRC) helices.

Main Methods: A rational strategy that integrates dynamics simulation, thermodynamics calculation, fluorescence polarization and circular dichroism is proposed to design HRC-targeted α-helical hairpin traps based on the crystal template of HRN core.

Key Findings: The designed hairpin traps possess a typical helix-turn-helix scaffold that can be stabilized by stapling a disulfide bridge across its helical arms, which are highly structured (helicity >60%) and can mimic the native spatial arrangement of HRN helices in TOH motif to trap the hotspot sites of HRC with effective affinity (K is up to 6.4 μM).

Significance: The designed α-helical hairpin traps can be used as lead entities for further developing TOH-disrupting agents to target RSV membrane fusion event and the proposed rational design strategy can be readily modified to apply for other type I viruses.