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).
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
- 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→|