Beta Trefoil

This architecture is formed from a capped beta barrel with an internal pseudo threefold symmetry.

The examples shown below are the agglutinin domain (CATH domain ID 1jlxA01), and acidic fibroblast growth factor (FGF-1) (CATH domain ID 1afcA00).

References

Three-fold structural pattern in the soybean trypsin inhibitor (Kunitz).
McLachlan AD
J Mol Biol133p557-63(1979 Oct 9)

beta-Trefoil fold. Patterns of structure and sequence in the Kunitz inhibitors interleukins-1 beta and 1 alpha and fibroblast growth factors.
Murzin AG, Lesk AM, Chothia C
J Mol Biol223p531-43(1992 Jan 20)