Structural and biological mimicry of protein surface recognition by α/β-peptide foldamers

Unnatural oligomers that can mimic protein surfaces offer a potentially useful strategy for blocking biomedically important proteinprotein interactions. Here we evaluate an approach based on combining α- and β-amino acid residues in the context of a polypeptide sequence from the HIV protein gp41, which represents an excellent testbed because of the wealth of available structural and biological information. We show that α/β-peptides can mimic structural and functional properties of a critical gp41 subunit. Physical studies in solution, crystallographic data, and results from cell-fusion and virus-infectivity assays collectively indicate that the gp41-mimetic α/β-peptides effectively block HIV-cell fusion via a mechanism comparable to that of gp41-derived α-peptides. An optimized α/β-peptide is far less susceptible to proteolytic degradation than is an analogous α-peptide. Our findings show how a two-stage design approach, in which sequence-based α→β replacements are followed by site-specific backbone rigidification, can lead to physical and biological mimicry of a natural biorecognition process.