De novo design of heterotrimeric coiled coils.

The three-helix bundle is a common structural motif among natural proteins. It has been observed in numerous important proteins, such as fibrinogen, laminin, spectrin, dystrofin, hemagglutinin, and mannose binding proteins. The three-helix bundle is a simple structure in which three alpha-helices pack against each other, with a slight left-handed twist. Because of its simplicity relative to other structural motifs, the three-helix bundle can be conveniently used both to clarify the forces responsible for the protein folding and stability, and for the design of novel proteins. In this paper we describe the design, synthesis, and characterization of three peptides that self-assemble into antiparallel, heterotrimeric coiled coils. The experimental results, obtained from CD spectroscopy and ultracentrifugation equilibrium sedimentation, indicate that the mixture of the three peptides preferentially forms heterotrimers; moreover, these aggregates represent attractive systems for combinatorial design of libraries of pseudo C3 symmetric ligands or binding sites.