De novo design of discrete, stable 310-helix peptide assemblies

The alpha-helix is pre-eminent in structural biology(1) and widely exploited in protein folding(2), design(3) and engineering(4). Although other helical peptide conformations do exist near to the alpha-helical region of conformational space-namely, 3(10)-helices and pi-helices(5)-these occur much less frequently in protein structures. Less favourable internal energies and reduced tendencies to pack into higher-order structures mean that 3(10)-helices rarely exceed six residues in length in natural proteins, and that they tend not to form normal supersecondary, tertiary or quaternary interactions. Here we show that despite their absence in nature, synthetic peptide assemblies can be built from 3(10)-helices. We report the rational design, solution-phase characterization and an X-ray crystal structure for water-soluble bundles of 3(10)-helices with consolidated hydrophobic cores. The design uses six-residue repeats informed by analysing 3(10)-helical conformations in known protein structures, and incorporates alpha-aminoisobutyric acid residues. Design iterations reveal a tipping point between alpha-helical and 3(10)-helical folding, and identify features required for stabilizing assemblies of 3(10)-helices. This work provides principles and rules to open opportunities for designing into this hitherto unexplored region of protein-structure space.

Automated summary

The alpha-helix is important in structural biology and protein folding. This study shows that synthetic peptide assemblies can be built from 3(10)-helices, which are less common in natural proteins. The research provides principles and rules for designing in this unexplored region of protein structure.