Chemical Catalysis by the Translocator Protein (18 kDa)

Translocator proteins (18 kDa) (TSPOs) are conserved integral membrane proteins. In both eukaryotes and prokaryotes, TSPOs interact with porphyrins, precursors of heme, and photosynthetic pigments. Here we demonstrate that bacterial TSPOs catalyze rapid porphyrin degradation in a light- and oxygen-dependent manner. The reaction is inhibited by a synthetic TSPO ligand PK11195 and by mutations of conserved residues, which affect either porphyrin binding or catalytic activity. We hypothesize that TSPOs are ancient enzymes mediating porphyrin catabolism with the consumption of reactive oxygen species.