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Abstract

Seventy years ago, Francis Crick introduced the coiled coil to account for the structural

properties of proteins referred to as ‘k-m-e-f’, for keratin, myosin, epidermin, and fibrinogen. His model envisaged 2 or 3 α-helices wound around each other in parallel orientation, systematically interlocking their side chains along the fiber in a pattern that would repeat every seven residues (the heptad repeat), specifying a supercoil of opposite handedness to that of the α-helix. Since then, the coiled-coil fold has been found to be vastly more diverse, encompassing structures of between two and more than 20 helices in parallel or antiparallel orientation, which may form fibers, levers, tubes, funnels, sheets, spirals, and rings. It covers periodicities leading to both left-handed and right-handed supercoils (and to straight helical bundles in between); and includes local departures from α-helical structure such as 310 -helices, π-turns, and even short β-strands, as in the α/β-coiled coils. Here we will describe how a few simple biophysical rules can produce such a seemingly endless diversity.