{{Short description|Protein fold}} thumb|Structure of the beta trefoil fold of Interleukin 1b. 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. Overall, this structure has an approximate three-fold symmetry.<ref name="pmid1738162">{{cite journal |vauthors=Murzin AG, Lesk AM, Chothia C |title= β-trefoil fold: patterns of structure and sequence in the kunitz inhibitors interleukins-1β and 1α and fibroblast growth factors|journal= Journal of Molecular Biology|volume= 223|issue= 2|pages= 531–43|date= Jan 1992|pmid= 1738162 |doi= 10.1016/0022-2836(92)90668-A}}</ref><ref name="pmid18650393">{{cite journal |vauthors=Gosavi S, Whitford PC, Jennings PA, Onuchic JN |title= Extracting function from a β-trefoil folding motif |journal= PNAS |volume= 105 |issue= 30 |pages= 10384–9 |date= Jul 2008 |pmid= 18650393|doi= 10.1073/pnas.0801343105 |pmc=2492465|bibcode= 2008PNAS..10510384G |doi-access= free }}</ref>
==Details== The hairpins are arranged in three β-β-β-loop-β sequences, each having a "Y" or trefoil-like structure. The first and fourth β strands form one hairpin, while the second and third form the other hairpin- each hairpin forms another arm of the "Y" and the long loop forms its trunk.<ref name="pmid1738162"/><ref name="pmid18650393"/>
The beta barrel has a 16 Å diameter, and is filled with amino acid side-chains. <ref name="pmid1738162"/>
==Occurrence== 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.<ref name="pmid1738162"/><ref name="pmid18650393"/>
==External links== * [http://www.cathdb.info/cathnode/2.80 CATH Architecture "Beta Trefoil"]
==References== {{reflist}}
Category:Protein folds