Proline

From FoldIt Wiki

Proline (P) is a particular amino acid, since its side chain forms a closed pentagon cycle with the backbone. It can be recognized easily because it looks like a handle on the backbone.

[edit] Notes

• This closed cycle enables only a little freedom of movement and usually bends the backbone. For example it can 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 helices or sheets, but is often found in the first turn of a helix.
• This amino acid is weakly hydrophobic; however, it is often found on the "water side" of the molecule.

More information can be found at http://en.wikipedia.org/wiki/Proline