Beta trefoil fold

In molecular biology the β trefoil fold is a protein fold that consists of six beta hairpins, each formed by two beta strands.

Together these form a beta barrel with a triangular "cap", each consisting of three hairpins.

[1][2] The hairpins are arranged in three β-β-β-loop-β sequences, each having a "Y" or trefoil-like structure.

[1][2] The beta barrel has a 16 Å diameter, and is filled with amino acid side-chains.

[1] Among other proteins, β trefoil fold is found in Kunitz inhibitors of several plants such as soybean, Erythrina afra and wheat; in members of the interleukin 1 cytokine family (interleukin-1 alpha, interleukin-1 beta and interleukin-1 receptor antagonist); and in fibroblast growth factors 1 and 2.