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.
Aspartic acid has poor helix-forming properties.
More information can be found at http://en.wikipedia.org/wiki/Aspartic_acid