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{{DISPLAYTITLE:3<sub>10</sub> helix}} | |||
[[Image:3 10 helix neg49 neg26 sideview.png|thumb|right|250px|Side view of a 3<sub>10</sub>-helix of [[alanine]] residues in [[atom]]ic detail. Two hydrogen bonds to the same peptide group are highlighted in magenta; the oxygen-hydrogen distance is 1.83 Å (183 pm). The [[protein]] chain runs upwards, i.e., its N-terminus is at the bottom and its C-terminus at the top of the figure. Note that the sidechains point slightly ''downwards'', i.e., towards the N-terminus.]] | |||
A '''3<sub>10</sub> helix''' is a type of [[secondary structure]] found (rarely) in [[protein]]s. | |||
==Structure== | |||
The amino acids in a 3<sub>10</sub>-helix are arranged in a right-handed [[helix|helical]] structure. Each amino acid corresponds to a 120° turn in the helix (i.e., the helix has three residues per turn), and a translation of 2.0 Å (= 0.2 nm) along the helical axis, and has 10 atoms in the ring formed by making the hydrogen bond. Most importantly, the [[amine|N-H]] group of an amino acid forms a [[hydrogen bond]] with the [[carbonyl|C = O]] group of the amino acid ''three'' residues earlier; this repeated ''i'' + 3 → ''i'' hydrogen bonding '''defines''' a 3<sub>10</sub>-helix. Similar structures include the [[Alpha_helix|α-helix]] (''i'' + 4 → ''i'' hydrogen bonding) and the [[Pi_helix|π-helix]] ''i'' + 5 → ''i'' hydrogen bonding). | |||
[[Image:310 helix topview.png|thumb|left|225px|Top view of the same helix shown to the right. Three [[carbonyl]] groups are pointing upwards towards the viewer, spaced roughly 120° apart on the circle, corresponding to 3.0 [[amino acid|amino-acid]] residues per turn of the helix.]] | |||
Residues in 3<sub>10</sub>-helices typically adopt (φ, ψ) [[dihedral angle]]s near (−49°, −26°). More generally, they adopt dihedral angles such that the ψ [[dihedral angle]] of one residue and the φ [[dihedral angle]] of the ''next'' residue sum to roughly −75°. For comparison, the sum of the dihedral angles for an α-helix is roughly −105°, whereas that for a π-helix is roughly −125°. | |||
The general formula for the rotation angle Ω per residue of any polypeptide helix with ''trans'' isomers is given by the equation | |||
:<math> | |||
3 \cos \Omega = 1 - 4 \cos^{2} \left(\frac{\varphi + \psi}{2} \right). | |||
</math> | |||
==See also== | |||
* [[alpha helix]] | |||
* [[pi helix]] | |||
* [[secondary structure]] | |||
==References== | |||
* Pauling L, Corey RB and Branson HR. (1951) "The Structure of Proteins: Two Hydrogen-Bonded Helical Configurations of the Polypeptide Chain", ''Proc. Nat. Acad. Sci. Wash.'', '''37''', 205. | |||
{{Protein secondary structure}} | |||
[[Category:Protein structural motifs]] | |||
[[Category:Helices]] | |||
{{protein-stub}} |
Revision as of 16:08, 27 February 2013
A 310 helix is a type of secondary structure found (rarely) in proteins.
Structure
The amino acids in a 310-helix are arranged in a right-handed helical structure. Each amino acid corresponds to a 120° turn in the helix (i.e., the helix has three residues per turn), and a translation of 2.0 Å (= 0.2 nm) along the helical axis, and has 10 atoms in the ring formed by making the hydrogen bond. Most importantly, the N-H group of an amino acid forms a hydrogen bond with the C = O group of the amino acid three residues earlier; this repeated i + 3 → i hydrogen bonding defines a 310-helix. Similar structures include the α-helix (i + 4 → i hydrogen bonding) and the π-helix i + 5 → i hydrogen bonding).
Residues in 310-helices typically adopt (φ, ψ) dihedral angles near (−49°, −26°). More generally, they adopt dihedral angles such that the ψ dihedral angle of one residue and the φ dihedral angle of the next residue sum to roughly −75°. For comparison, the sum of the dihedral angles for an α-helix is roughly −105°, whereas that for a π-helix is roughly −125°.
The general formula for the rotation angle Ω per residue of any polypeptide helix with trans isomers is given by the equation
See also
References
- Pauling L, Corey RB and Branson HR. (1951) "The Structure of Proteins: Two Hydrogen-Bonded Helical Configurations of the Polypeptide Chain", Proc. Nat. Acad. Sci. Wash., 37, 205.