Alanine (ALA or A) is a hydrophobic amino acid. It is the smallest amino acid except for glycine. Its shape is distinctive on Foldit.
Alanine 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 "a" for alanine.
For more, see Alanine on wikipedia.