An alpha/beta barrel is a protein fold formed by units composed of a short

α-helix An alpha helix (or α-helix) is a sequence of amino acids in a protein that are twisted into a coil (a helix). The alpha helix is the most common structural arrangement in the Protein secondary structure, secondary structure of proteins. It is al ...

followed by two anti-parallel β-strands, followed by an α-helix and a β-strand; the three β-strands form a

β-sheet The beta sheet (β-sheet, also β-pleated sheet) is a common structural motif, motif of the regular protein secondary structure. Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone chain, backbon ...

that runs parallel to the barrel and the α-helix is in the outside of the barrel but does not contact the α-helices of the other repeats like in TIM barrels. The protein structures known for this fold come proteins from the eukaryotic and archaeal initiation factor 6 family, namely the '' Methanococcus jannaschii'' aIF6 and ''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungal microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have be ...

'' eIF6, and from the eIF6 from ''

Dictyostelium discoideum ''Dictyostelium discoideum'' is a species of soil-dwelling Amoeboid, amoeba belonging to the phylum Amoebozoa, infraphylum Mycetozoa. Commonly referred to as slime mold, ''D. discoideum'' is a eukaryote that transitions from a collection of unic ...

''. These alpha/beta barrels are commonly occurring motifs constructed from repetitions of the beta-alpha-beta loop motif. This alpha/beta barrel is a domain of pyruvate kinase enzyme.

References

{{reflist Protein structure Protein folds Protein tandem repeats Protein domains