1. Department of Bioengineering and Computer Science Department, APM 3832, University of CaliforniaSan Diego, 9500 Gilman Drive, La Jolla, California 92093-0114, Protein Chemistry Laboratory, Alliance for Cellular Signaling, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9196, and Keck School of Medicine, University of Southern California, 1441 Eastlake Avenue, Los Angeles, California 90033