Effect of specific amino acid substitutions in the putative fusion peptide of structural glycoprotein E2 on Classical Swine Fever Virus replication

•A putative fusion peptide (FP) region in CSFV E2 protein was shown to be critical for virus growth.•Synthetic FPs were shown to efficiently penetrate into lipid membranes using an in vitro model.•Individual residues in the FP affecting virus replication were identified by reverse genetics.•The same FP residues are also responsible for mediating membrane fusion.

E2, along with Erns and E1, is an envelope glycoprotein of Classical Swine Fever Virus (CSFV). E2 is involved in several virus functions: cell attachment, host range susceptibility and virulence in natural hosts. Here we evaluate the role of a specific E2 region, 818CPIGWTGVIEC828, containing a putative fusion peptide (FP) sequence. Reverse genetics utilizing a full-length infectious clone of the highly virulent CSFV strain Brescia (BICv) was used to evaluate how individual amino acid substitutions within this region of E2 may affect replication of BICv. A synthetic peptide representing the complete E2 FP amino acid sequence adopted a β-type extended conformation in membrane mimetics, penetrated into model membranes, and perturbed lipid bilayer integrity in vitro. Similar peptides harboring amino acid substitutions adopted comparable conformations but exhibited different membrane activities. Therefore, a preliminary characterization of the putative FP 818CPIGWTGVIEC828 indicates a membrane fusion activity and a critical role in virus replication.