Beta helix

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

Two-stranded helices[edit]

The simplest beta helix contains two "layers" of beta sheets connected by glycine-rich six-residue loops that invariably contain an aspartate to bind one calcium ion per loop. Each layer consists of a nearly-planar series of parallel hydrogen-bonded beta strands and the two layers together enclose a hydrophobic core.

Three-stranded helices[edit]

Three-stranded beta helices form a distorted triangular prism shape in which each face exhibits parallel inter-strand hydrogen bonding. One of the three sheets that form the repeating structural motif can appear "bent" relative to the other two, which face each other as in the two-stranded helix. Two of the three linking loops between the sheets can be of arbitrary length and can even contain other structural domains; the third is restricted to two residues. A characteristic common hexapeptide repeat found in both left- and right-handed helices is the sequence \mathrm{[LIV]-[GAED]-X_{2}-[STAV]-X}. Known three-stranded helices are appreciably longer than their two-stranded counterparts.

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.

Four-stranded helices[edit]

Members of the Pentapeptide repeat family have been shown to possess a quadrilateral beta-helix structure.[4]

References[edit]

  1. ^ 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. PMC 450161. PMID 8665839. 
  2. ^ 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. doi:10.1038/35018604. PMID 10917536. 
  3. ^ 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. 
  4. ^ 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. 
  • 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[edit]