OPM provides spatial arrangements of membrane proteins with respect to the hydrocarbon core of the lipid bilayer. Archaeal, bacterial (gramĀ±), chloroplast, ER, endosome, eukaryotic PM, Golgi, lysosome, mitochondrial (inner/outer), nuclear (inner/outer), peroxisome, secreted proteins, thylakoid, vacuole, vesicle, viral.