The Purification of Heme Peroxidases from Escherichia coli Inclusion Bodies: A Success Story Shown by the Example of Horseradish Peroxidase

In the following chapter a purification process for recombinant Horseradish peroxidase (HRP) produced in Escherichia coli is described. This enzyme is a secretory plant oxidoreductase belonging to the large peroxidase family III within the peroxidase-catalase superfamily of enzymes. It has high biotechnological significance, however, the isolation of the enzyme from its natural source, the horseradish root, has several shortcomings, which makes the development of a recombinant production strategy interesting. The presented protocol covers all process steps from isolation to the final chromatography step; the enzyme is solubilized from insoluble inclusion bodies, refolded and concentrated to yield a high purity enzyme preparation which is comparable to the commercially available plant-derived HRP. Moreover, we believe that this procedure can also be used to process other peroxidases of family II and III of the plant peroxidase superfamily, as they all share the same relevant features like disulfide bonds and a heme group.

Different fungal peroxidases oxidize nitrophenols at a surface catalytic tryptophan

Dye-decolorizing peroxidase (DyP) from Auricularia auricula-judae and versatile peroxidase (VP) from Pleurotus eryngii oxidize the three mononitrophenol isomers. Both enzymes have been overexpressed in Escherichia coli and in vitro activated. Despite their very different three-dimensional structures, the nitrophenol oxidation site is located at a solvent-exposed aromatic residue in both DyP (Trp377) and VP (Trp164), as revealed by liquid chromatography coupled to mass spectrometry and kinetic analyses of nitrophenol oxidation by the native enzymes and their tryptophan-less variants (the latter showing 10-60 fold lower catalytic efficiencies).

Characterisation of peroxidasin activity in isolated extracellular matrix and direct detection of hypobromous acid formation

Peroxidasin is a heme peroxidase that catalyses the oxidation of bromide by hydrogen peroxide to form an essential sulfilimine cross-link between methionine and hydroxylysine residues in collagen IV. We investigated cross-linking by peroxidasin embedded in extracellular matrix isolated from cultured epithelial cells and its sensitivity to alternative substrates and peroxidase inhibitors. Peroxidasin showed peroxidase activity as measured with hydrogen peroxide and Amplex red. Using a specific mass spectrometry assay that measures NADH bromohydrin, we showed definitively that the enzyme releases hypobromous acid (HOBr). Less than 1 μM of the added hydrogen peroxide was used by peroxidasin. The remainder was consumed by catalase activity that was associated with the matrix. Results from NADH bromohydrin measurements indicates that low micromolar HOBr generated by peroxidasin was sufficient for maximum sulfilimine cross-linking, whereas 100 μM reagent HOBr or taurine bromamine was less efficient. This implies selectivity for the enzymatic process. Physiological concentrations of thiocyanate and urate partially inhibited cross-link formation. 4-Aminobenzoic acid hydrazide, a commonly used myeloperoxidase inhibitor, also inhibited peroxidasin, whereas acetaminophen and a 2-thioxanthine were much less effective. In conclusion, HOBr is produced by peroxidasin in the extracellular matrix. It appears to be directed at the site of collagen IV sulfilimine formation but the released HOBr may also undergo other reactions.