Aspartic acid (ASP or D), usually referred to as aspartate in Foldit, is a hydrophilic amino acid. Its shape in Foldit is distinguishable from asparagine, to which it is closely related, only with the CPK or EnzDes coloring options (found in view options). Aspartate can also be confused with theonine.
Aspartate has poor helix-forming properties.
Aspartate's sidechain contains two oxygen atoms which can act as hydrogen bond acceptors. The end of the sidechain is a carboxyl group, the same structure found in the backbone of amino acids. The carboxyl group means aspartate's sidechain is formally considered acidic. See the Sidechain Bonding Gallery and the Sidechain Bonding Table for other sidechain donors and acceptors.
For more, see Aspartic acid on wikipedia.