Lysine / LYS / K (EnzDes coloring
Lysine (LYS or K) is a hydrophilic amino acid. Its shape in Foldit is unique. It's longer than methionine.
Lysine has a tendency to form part of a helix, as part of the "MALEK" group of amino acids.
In the Foldit Lua interface, the functions structure.GetAminoAcid and structure.SetAminoAcid use lowercase "k" for lysine.
Lysine's sidechain contains a nitrogen atom, which can act as hydrogen bond donor.
Lysine's sidechain contains a nitrogen atom which can act as hydrogen bond donor. The end of the sidechain is a amino group, the same structure found in the backbone of amino acids. The carboxyl group means Lysine's sidechain is formally considered basic. See the Sidechain Bonding Gallery and the Sidechain Bonding Table for other sidechain donors and acceptors.
For more, see Lysine on wikipedia.