Helices in Proteins

Helical conformations in proteinsHelical conformations in proteins

This page illustrates the 3 most common helical conformations (among secondary structures) found in proteins.

Each of the three examples below is a decapeptide fragment extracted from an actual protein structure in the PDB. They are shown using the same scale, for a better comparison (as a consequence, zoom in the Jmol applets is disabled).

To re-align the 3 models, reload this page.

310 helix	alpha helix	pi helix
spinqualitylabelsall models PDB ID 3L79_514-525.pdb Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image	spinqualitylabelsall models PDB ID 1HHO_B_5-16.pdb Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image	spinqualitylabelsall models PDB ID 2QD3_A_346-357.pdb Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image
3 residues/turn rise 0.20 nm/residue helix pitch 0.60 nm H bonds: Ni+3 → Oi φ = -49°, ψ = -26° 3l79: 514-525	3.6 residues/turn rise 0.15 nm/residue helix pitch 0.54 nm H bonds: Ni+4 → Oi φ = -60°, ψ = -45° 1hho chain B: 5-16	4.4 residues/turn rise ~0.115 nm/residue helix pitch ~0.41 nm H bonds: Ni+5 → Oi φ = -55°, ψ = -70° (approx.) 2qd3 chain A: 346-357

The alpha helix is by far the most common helix. Note that it is a right-handed helix when formed with the common L-amino acids. (It is left-handed when formed with D-amino acids.) When viewed from either end, right-handed helices turn clockwise when followed away from you.

See AlsoSee Also

• Alpha helix at Wikipedia.
• Secondary structure
• Protein primary, secondary, tertiary and quaternary structure (slides for teaching)
• Estructuras primaria, secundaria, terciaria y cuaternaria de las proteínas (en formato de presentación)