Toward β-amino acid proteins:: A cooperatively folded β-peptide quaternary structure

Folded polymers in nature are assembled from simple monomers and adopt complex folded structures through networks of stabilizing noncovalent interactions. These interactions define secondary and tertiary structure and in most cases specify a unique three-dimensional architecture. Individual secondary or tertiary structures can also associate with one another to form multi-subunit quaternary structures. Nonnatural folded polymers have potential for similar structural versatility. Here we describe a pair of β3-peptides whose sequences were designed to promote a 14-helix structure in water, favor hetero-oligomer formation, and disfavor nonspecific aggregation. These β3-peptides assemble noncovalently into a well-defined hetero-oligomer characterized by a defined stoichiometry, a highly stabilized secondary structure, and a cooperative melting transition (TM > 55 °C). This work demonstrates that β3-peptides can assemble into defined, cooperatively folded quaternary structures and constitutes an important step toward designing protein-like assemblies from nonnatural polymers. Copyright © 2006 American Chemical Society.