Chikungunya virus E1 fusion loop-membrane interaction: Conserved residues and shallow insertion

Area of Science:

• Virology
• Structural Biology
• Membrane Biophysics

Background:

• Viral fusion proteins mediate membrane fusion for enveloped virus entry.
• Class I fusion proteins have well-characterized fusion peptides, but class II fusion loops remain less understood.
• The chikungunya virus (CHIKV) E1 glycoprotein is a class II fusion protein.

Purpose of the Study:

• To investigate the conserved sequence and structural features of the CHIKV E1 fusion loop.
• To elucidate the mechanism of membrane interaction and fusion promotion by class II fusion loops.

Main Methods:

• Molecular dynamics (MD) simulations (atomistic and coarse-grained)
• Mutational analysis of conserved residues (G83, W89)
• Depth-dependent fluorescence quenching (parallax method)
• Liposome fusion assays
• Langmuir monolayer experiments

Main Results:

• Comparative analysis identified conserved N-terminal glycine and loop-tip tryptophan in class II fusion loops.
• MD simulations showed shallow insertion and tilted interfacial orientation of the E1 fusion loop, stabilized by hydrogen bonding.
• Tryptophan fluorescence quenching confirmed Trp89 localization at the lipid headgroup-acyl chain boundary.
• G83A mutation abolished membrane insertion and fusion; W89A mutation retained near wild-type activity.
• E1 protein altered lipid packing, with reduced effect for W89A mutant, indicating contributions of both G83 and W89 to membrane destabilization.

Conclusions:

• Class II fusion loops utilize shallow, interfacial anchoring mediated by conserved residues (e.g., G83, W89).
• This binding mode perturbs lipid organization to promote fusion.
• Class II fusion mechanism differs from the deeper-penetrating peptides of class I fusion proteins.