Monomeric, left-handed β-helix antifreeze protein from the spruce budworm Choristoneura fumiferana (PDB: 1M8N​).
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.
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 strands 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.

Both pectate lyase and P22 tailspike protein contain right-handed helices; left-handed versions have been observed in enzymes such as UDP-N-acetylglucosamine acyltransferase and archaeal carbonic anhydrase.[5] Other proteins that contain beta helices include the antifreeze proteins from the beetle Tenebrio molitor (right-handed)[6] and from the spruce budworm, Choristoneura fumiferana (left-handed),[7] where regularly spaced threonines on the β-helices bind to the surface of ice crystals and inhibit their growth.

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]

References

  1. ^ "CATH database - folds and homologous superfamilies within the beta 2-solenoid architecture". CATH database.
  2. ^ "CATH database - folds and homologous superfamilies within the beta 3-solenoid architecture". CATH database. Archived from the original on 26 July 2011.
  3. ^ 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.
  4. ^ "Double-stranded beta-helix". SCOPe. Retrieved 29 November 2021.
  5. ^ Kisker C, Schindelin H, Alber BE, Ferry JG, Rees DC (May 1996). "A left-hand beta-helix revealed by the crystal structure of a carbonic anhydrase from the archaeon Methanosarcina thermophila". EMBO J. 15 (10): 2323–30. doi:10.1002/j.1460-2075.1996.tb00588.x. PMC 450161. PMID 8665839.
  6. ^ Liou YC, Tocilj A, Davies PL, Jia Z (July 2000). "Mimicry of ice structure by surface hydroxyls and water of a beta-helix antifreeze protein". Nature. 406 (6793): 322–4. Bibcode:2000Natur.406..322L. doi:10.1038/35018604. PMID 10917536. S2CID 4385352.
  7. ^ Leinala EK, Davies PL, Jia Z (May 2002). "Crystal structure of beta-helical antifreeze protein points to a general ice binding model". Structure. 10 (5): 619–27. doi:10.1016/s0969-2126(02)00745-1. PMID 12015145.
  8. ^ Vetting MW, Hegde SS, Fajardo JE, et al. (January 2006). "Pentapeptide repeat proteins". Biochemistry. 45 (1): 1–10. doi:10.1021/bi052130w. PMC 2566302. PMID 16388575.