Recent improvements in de novo protein design are likely to support a broad range of applications, but larger complexes will be easier to create if a building block approach is adopted. Now protein filaments with tunable geometry can be made using assemblies that have both cyclic and superhelical symmetries aligned along the same axis.

Symmetry plays an important role in understanding protein structures, especially complexes built from many copies of the same polypeptide. Cyclic symmetry is closed, meaning that repeating the operator relating one subunit to its neighbour eventually returns to the starting point. Open symmetry can extend a structure indefinitely, either by simple translation or by combined rotation and translation. If the rotation and translation are always the same between repeats, then a regular helix results. Superhelical symmetry is the most general form of open symmetry, with no fixed operator between repeats, and this is the type of symmetry generally found between the tandemly repeated motifs of repeat proteins. DHR proteins are rigid and easily decorated with other protein domains, but the key point of the new designs, which the Baker group named cyclic helical repeat proteins (CHRs), is that both symmetry elements share the same axis.