Gradišar, H. et al. Nat. Chem. Biol. doi:10.1038/nchembio.1248 (28 April 2013).

Fletcher, J.M. et al. Science 340, 595–599 (2013).

A variety of DNA-based nanostructures have been created by researchers taking advantage of base complementarity to rationally design folds. The engineering of polypeptide-based nanostructures is more challenging owing to the broader chemical diversity of amino acids, but this diversity should also permit greater design flexibility. Gradišar et al. report the design of a self-assembling tetrahedron (of about 7 nanometers in diameter) from a single polypeptide chain containing concatenated coiled-coil dimer-forming segments interspersed with flexible regions. Fletcher et al. describe design rules for forming large, spherical cages (of about 100 nanometers in diameter) self-assembled from a carefully chosen set of coiled-coil peptides. Such polypeptide-based nanostructures could be used for applications such as drug delivery or, in the case of the spherical cages, as potential 'protocells' in synthetic biology.