Monomeric, left-handed β-helix antifreeze protein from the spruce budworm Choristoneura fumiferana (PDB: 1M8N).Dimeric, right-handed β-helix antifreeze protein from the beetle Tenebrio molitor (PDB: 1EZG). Face-to-face association of β-helices.
A beta helix is a tandem protein repeat structure formed by the association of parallel beta sheet in a helical pattern with either two[1] or three[2] faces. The beta helix is a type of solenoid protein domain. The structure is stabilized by inter-strand hydrogen bonds, protein-protein interactions, and sometimes bound metal ions. Both left- and right-handed beta helices have been identified. These structures are distinct from jelly-roll folds, a different protein structure sometimes known as a "double-stranded beta helix".[3][4]
The first beta-helix was observed in the enzyme pectate lyase, which contains a seven-turn helix that reaches 34 Å (3.4 nm) long. The P22 phage tail spike protein, a component of the P22 bacteriophage, has 13 turns and in its assembled homotrimer is 200 Å (20 nm) in length. Its interior is close-packed with no central pore and contains both hydrophobic residues and charged residues neutralized by salt bridges.
Beta helices can associate with each other effectively, either face-to-face (mating the faces of their triangular prisms) or end-to-end (forming hydrogen bonds). Hence, β-helices can be used as "tags" to induce other proteins to associate, similar to coiled coil segments.
Members of the pentapeptide repeat family have been shown to possess a quadrilateral beta-helix structure.[8]
^Aik, WeiShen; McDonough, Michael A; Thalhammer, Armin; Chowdhury, Rasheduzzaman; Schofield, Christopher J (December 2012). "Role of the jelly-roll fold in substrate binding by 2-oxoglutarate oxygenases". Current Opinion in Structural Biology. 22 (6): 691–700. doi:10.1016/j.sbi.2012.10.001. PMID23142576.
