New currency for old rope: from coiled-coil assemblies to α-helical barrels

α-Helical coiled coils are ubiquitous protein–protein-interaction domains. They share a relatively straightforward sequence repeat, which directs the folding and assembly of amphipathic α-helices. The helices can combine in a number of oligomerisation states and topologies to direct a wide variety of protein assemblies. Although in nature parallel dimers, trimers and tetramers dominate, the potential to form larger oligomers and more-complex assemblies has long been recognised. In particular, complexes above pentamer are interesting because they are barrel-like, having central channels or pores with well-defined dimensions and chemistry. Recent empirical and rational design experiments are beginning to chart this potential new territory in coiled-coil space, leading to intriguing new structures, and possibilities for functionalisation and applications.

► α-Helical coiled coils are ubiquitous protein–protein-interaction domains.
► Dimers, trimers and tetramers dominate, but more-complex assemblies are possible.
► Understanding sequence-to-structure relationships for these states is improving.
► Pentamers and above are barrel-like with central channels or pores.
► Recent studies show that de novo hexamers that can be internally functionalised.