# 310 helix

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File:3 10 helix neg49 neg26 sideview.png
Side view of an 310-helix of alanine residues in atomic 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 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. 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).

File:310 helix topview.png
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 residues per turn of the helix.

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

${\displaystyle 3\cos \Omega =1-4\cos ^{2}\left({\frac {\varphi +\psi }{2}}\right).}$

## 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
Helices: α-helix | 310 helix | π-helix | β-helix | Polyproline helix | Collagen helix
Extended: β-strand | Turn | Beta hairpin | Beta bulge | α-strand
Supersecondary: Coiled coil | Helix-turn-helix | EF hand
Secondary structure propensities of amino acids
Helix-favoring: Methionine | Alanine | Leucine | Glutamic acid | Glutamine | Lysine
Extended-favoring: Threonine | Isoleucine | Valine | Phenylalanine | Tyrosine | Tryptophan
Disorder-favoring: Glycine | Serine | Proline | Asparagine | Aspartic acid
No preference: Cysteine | Histidine | Arginine
←Primary structure Tertiary structure→