Tryptophan / TRP / W (EnzDes coloring)
Tryptophan (TRP or W) is one of the more hydrophobic amino acids. Its double-ring shape is unique in Foldit.
In the Foldit Lua interface, the functions structure.GetAminoAcid and structure.SetAminoAcid use lowercase "w" for tryptophan.
The double ring structure is known as indole, consisting of a six-sided benzene ring and a five-sided pyrrole. The pyrrole ring contains one nitrogen atom and four carbon atoms.
For more, see tryptophan on wikipedia.
Vijay Pande of Folding@home wrote a piece on tryptophan on his blog: On turkey and tryptophan.