The present invention provides proteins capable of modulating or mediating the FAS receptor ligand or TNF effect on cells carrying FAS receptor or p55 receptor by binding or interacting with MORT-1 protein, which in turn binds to the intracellular domain of the FAS receptor or to another protein TRADD which binds to the p55 receptor. In addition, peptide inhibitors which interfere with the proteolytic activity of MORT-1-binding proteins having proteolytic activity are provided as well as a method of designing them.
