During the development of SCOP22, we have identified a new, previously unrecognised type of alpha-alpha superhelix. Unlike other alpha-alpha superhelices, it is made of repetitive units smaller than one turn of the superhelix. There are approximately 2.5 units per turn of superhelix, with each unit forming a single 12-residue alpha-helix connected to the next helix without additional linker residues. The helix is amphipathic one, with the N- and C-ends being aligned with the non-polar face of the helix. Apart of these features, there is no associated sequence motif showing a strong preference for a particular aminoacid residue in a particular position within the dodecapeptide repeat.
This new motif is found so far in the two different proteins, MgtE and FliG. In the former, there is a continuous superhelix in the N-terminal region, whereas in the latter, the superhelix is fragmented into different structural domains, which come together as a result of conformational changes accompanying the protein function.