Well having looked into it further since I originally asked, and having been directed by several replies on the subject, it appears that at least one of the myriad caspase enzymes cleaves proteins at certains aspartate and cysteine residues. In fact I found this explanation of the name: CASPASES: Cysteine Aspartate Specific ProteASEs.
(see http://makeashorterlink.com/?L58432BA6)

Aspartame is a sweetener that goes by the trade name Nutrasweet that contains the amino acid aspartate.