title: Is dihydrolipoic acid among the reductive activators of parasite CysHis proteases?
abstract: Activities of mature CysHis proteases depend upon relative rates of oxidations vs. reductions of catalytic sulfur by multiple enzymatic and non-enzymatic reactions. CysHis peptidolysis is inhibited by Fe3+ but not Fe2+. Others report the paradox that malarial parasites require exogenous free lipoic acid (LA) from human host, although the apicoplast organelle produces it. Extra-cellular LA disulfide can be taken up and reduced to dihydrolipoic acid (DHLA) by reductases of any cell type. Here, the opposing effects of DHLA vs. Fe3+ on the falcipain-2 hemoglobinase were investigated employing Z-Phe-Arg-AMC substrate. Despite limited solubility, non-regenerated DHLA (10 microM, threshold 2 microM) was found to be the most potent activator of the air-inactivated (sulfoxygenated) protease discovered thus far. Activation was preemptively opposed by Fe3+, but not Fe2+. However, cruzain from T. cruzi, and cathepsin B from mammal were indistinguishable in their responsiveness to DHLA and Fe redox. Thus, DHLA activation vs. Fe3+ inhibition is not unique to falcipain-2 or apicomplexans but is rather a primordial feature of CysHis peptidolysis. Free LA and/or unassociated lipoylated enzyme subunits could be among multiple pathways shuttling reducing equivalents to reduction of proteins, including CysHis proteases. It is discussed that opposing DHLA-Fe3+ modification of plasmodial proteolysis might be a specialized adaptation to intra-erythrocytic growth.
authors: Department of Pharmacology and Toxicology, School of Medicine, Wright State University, Dayton, OH 45435, USA. thomas.lockwood@wright.edu
authors: Thomas D
authors: TD
authors: Lockwood
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D002401:Cathepsin B / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004793:Enzyme Reactivators / Q000494:pharmacology; D005978:Glutathione / Q000494:pharmacology; D006639:Histidine / Q000378:metabolism; D007501:Iron / Q000494:pharmacology; D008322:Mammals; D010084:Oxidation-Reduction; D010963:Plasmodium falciparum / Q000201:enzymology; D015800:Protozoan Proteins / Q000378:metabolism; D008063:Thioctic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D014349:Trypanosoma cruzi / Q000187:drug effects / Q000201:enzymology
chemical_list: D000975:Antioxidants; D004793:Enzyme Reactivators; D015800:Protozoan Proteins; D006639:Histidine; D008063:Thioctic Acid; C015144:dihydrolipoic acid; D007501:Iron; D003546:Cysteine Endopeptidases; C074032:cruzain, Trypanosoma cruzi; C416224:falcipain 2; D002401:Cathepsin B; D005978:Glutathione; D003545:Cysteine; D004229:Dithiothreitol