Chicago Medical School 1 article published in JoVE Biology Determining Membrane Protein Topology Using Fluorescence Protease Protection (FPP) Carl White1, Alex Nixon1, Neil A. Bradbury1 1Department of Physiology and Biophysics, Chicago Medical School Here, we present a protocol to determine the orientation and topology of integral membrane proteins in living cells. This simple protocol relies on selective protease sensitivity of chimeras between the protein of interest and GFP.