Effects of single α-to-β residue replacements on recognition of an extended segment in a viral fusion protein

Partial replacement of α-amino acid residues with β-amino acid residues has been established as a strategy for preserving target-engagement by helix-forming polypeptides while altering other properties. The impact of β-residue incorporation within polypeptides that adopt less regular conformations, however, has received less attention. The HRC domains of fusion glycoproteins from pathogenic paramyxoviruses contain a segment that must adopt an extended conformation in order to co-assemble with the HRN domain in the post-fusion state and drive merger of the viral envelope with a target cell membrane. Here we examine the impact of single α-to-β substitutions within this extended N-terminal segment of an engineered HRC peptide designated VIQKI. Stabilities of hexameric co-assemblies formed with the native HPIV3 HRN have been evaluated, the structures of five co-assemblies have been determined, and antiviral efficacies have been measured. Many sites within the extended segment show functional tolerance of α-to-β substitution. These results offer a basis for future development of paramyxovirus infection inhibitors with novel biological activity profiles, possibly including resistance to proteolysis.