Beta helix

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File:1m8n Choristoneura fumiferana.png
Monomeric, left-handed β-helix antifreeze protein from the spruce budworm Choristoneura fumiferana (PDB accession code 1M8N).
File:1ezg Tenebrio molitor.png
Dimeric, right-handed β-helix antifreeze protein from the beetle Tenebrio molitor (PDB accession code 1EZG). Face-to-face association of β-helices.

A beta helix is a protein structure formed by the association of parallel beta strands in a helical pattern with either two or three 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.

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 tailspike 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.[1] Other proteins that contain beta helices include the antifreeze proteins from the beetle Tenebrio molitor (right-handed)[2] and from the spruce budworm, Choristoneura fumiferana (left-handed),[3] 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.[4]

References

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  • Branden C, Tooze J. (1999). Introduction to Protein Structure 2nd ed. Garland Publishing: New York, NY. pp 84–6.
  • Dicker IB and Seetharam S. (1992) "What is known about the structure and function of the Escherichia coli protein FirA?" Mol. Microbiol., 6, 817-823.
  • Raetz CRH and Roderick SL. (1995) "A Left-Handed Parallel β Helix in the Structure of UDP-N-Acetylglucosamine Acyltransferase", Science, 270, 997-1000. (Left-handed)
  • Steinbacher S, Seckler R, Miller S, Steipe B, Huber R and Reinemer P. (1994) "Crystal structure of P22 tailspike protein: interdigitated subunits in a thermostable trimer", Science, 265, 383-386. (Right-handed)
  • Vaara M. (1992) "Eight bacterial proteins, including UDP-N-acetylglucosamine acyltransferase (LpxA) and three other transferases of Escherichia coli, consist of a six-residue periodicity theme", FEMS Microbiol. Lett, 97, 249-254.
  • Yoder MD, Keen NT and Jurnak F. (1993) "New domain motif:the structure of pectate lyase C, a secreted plant virulence factor", Science, 260, 1503-1507. (Right-handed)

External links

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