title: Bacitracin is not a specific inhibitor of protein disulfide isomerase.
abstract: To successfully dissect molecular pathways in vivo, there is often a need to use specific inhibitors. Bacitracin is very widely used as an inhibitor of protein disulfide isomerase (PDI) in vivo. However, the specificity of action of an inhibitor for a protein-folding catalyst cannot be determined in vivo. Furthermore, in vitro evidence for the specificity of bacitracin for PDI is scarce, and the mechanism of inhibition is unknown. Here, we present in vitro data showing that 1 mM bacitracin has no significant effect on the ability of PDI to introduce or isomerize disulfide bonds in a folding protein or on its ability to act as a chaperone. Where bacitracin has an effect on PDI activity, the effect is relatively minor and appears to be via competition of substrate binding. Whereas 1 mM bacitracin has minimal effects on PDI, it has significant effects on both noncatalyzed protein folding and on other molecular chaperones. These results suggest that the use of bacitracin as a specific inhibitor of PDI in cellular systems requires urgent re-evaluation.
authors.affiliation: Biocenter Oulu and Department of Biochemistry, University of Oulu, Oulu, Finland.
authors.forename: Anna-Riikka
authors.initials: AR
authors.lastname: Karala
authors.forename: Lloyd W
authors.initials: LW
authors.lastname: Ruddock
mesh_terms: D001414:Bacitracin / Q000494:pharmacology*; D001667:Binding, Competitive; D020134:Catalytic Domain; D004220:Disulfides / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007536:Isomerism; D007700:Kinetics; D046911:Macromolecular Substances / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011489:Protein Denaturation; D019704:Protein Disulfide-Isomerases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D017510:Protein Folding; D013884:Thiosulfate Sulfurtransferase / Q000737:chemistry / Q000378:metabolism
chemical_list: D004220:Disulfides; D004791:Enzyme Inhibitors; D046911:Macromolecular Substances; D010455:Peptides; D001414:Bacitracin; D013884:Thiosulfate Sulfurtransferase; D019704:Protein Disulfide-Isomerases