Proline / PRO / P (EnzDes coloring)

Proline (PRO or P) is an unusual amino acid, since its sidechain forms a closed pentagonal cycle with the backbone. It can be recognized easily because it looks like a handle on the backbone.

In the Foldit Lua interface, the functions structure.GetAminoAcid and structure.SetAminoAcid use lowercase "p" for proline.

For more, see Proline on wikipedia.


  • This closed cycle enables only a little freedom of movement and usually bends the backbone. For example, it can often be found in a short strand that links two strands of a sheet.
  • The cycle formed forbids any hydrogen bond of the backbone: thus it is almost never found within helixes or sheets, but is often found in the first turn of a helix.
  • This amino acid is weakly hydrophobic, but is often found on the "water side" of the molecule.