In this mainly beta fold, the polypeptide chain is wound into a large right-handed coil (or super helix). There are two different types of beta helix, one with two beta sheets, and one with three beta sheets. In our classification scheme we describe these as 2-solenoid and 3-solenoid beta architectures, respectively.

2-solenoid

This architecture comprises of two flat beta sheets packed tightly against one another. It has a highly distinctive and repetitive strand connectivity, which distinguishes it from the two layer sandwich architecture. The chain continually alternates between the two sheet layers whilst progressing in a spiraling motion from one end of the structure to the other, hence the term 'solenoid.' This could also be classified as a 2-layer beta sandwich but its unusual lack of curvature and its unusual topology have led to it being identified separately.

3-solenoid

Structures with this architecture comprise three beta sheets which have a distinctive strand connectivity. The chain visits each sheet in turn and is progressively wound around the principal axis in the same direction.