Peptidase_M48 is the largely extracellular catalytic region of CAAX prenyl protease homologs such as Human FACE-1 protease. These are metallopeptidases, with the characteriztic HExxH motif giving the two histidine-zinc-ligands and an adjacent glutamate on the next helix being the third. The whole molecule folds to form a deep groove/cleft into which the substrate can fit.