1. From the Center for Research in Biological Systems (M.H., T.H., Y.E.J., M.H.E.), the Department of Medicine (M.H., Z.F., Y.G., N.D.D., F.L.P., J.R.), National Center for Microscopy and Imaging Research (T.H., Y.E.J., M.H.E.), University of California San Diego, La Jolla, Calif; and the Division of Molecular Pharmaceutics (X.X.), University of North Carolina Eshelman School of Pharmacy, Chapel Hill, NC.