Biology:Beta helix

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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.

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.". http://www.cathdb.info/cathnode/2.150. 
  2. ↑ "CATH database - folds and homologous superfamilies within the beta 3-solenoid architecture.". http://www.cathdb.info/cathnode/2.160. 
  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. PMID 23142576. 
  4. ↑ "Double-stranded beta-helix". http://scop.berkeley.edu/sunid=51181. 
  5. ↑ "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. May 1996. doi:10.1002/j.1460-2075.1996.tb00588.x. PMID 8665839. 
  6. ↑ "Mimicry of ice structure by surface hydroxyls and water of a beta-helix antifreeze protein". Nature 406 (6793): 322–4. July 2000. doi:10.1038/35018604. PMID 10917536. Bibcode: 2000Natur.406..322L. 
  7. ↑ "Crystal structure of beta-helical antifreeze protein points to a general ice binding model". Structure 10 (5): 619–27. May 2002. doi:10.1016/s0969-2126(02)00745-1. PMID 12015145. 
  8. ↑ "Pentapeptide repeat proteins". Biochemistry 45 (1): 1–10. January 2006. doi:10.1021/bi052130w. PMID 16388575. 

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