Soluble expression of horseradish peroxidase in Escherichia coli and its facile activation.

Horseradish peroxidase (HRP) is widely used as a marker enzyme in immunoassays and biosensors, and can possibly be used in industries such as waste water treatments or fine chemical synthesis. Cost-effective production of active HRP is thus very important in the related fields. Also, engineering of HRP for its better performance in the designated application is expected to make the enzyme even more important in several areas of research and industry. One of obstacles to this end and to the large scale production of the enzyme has been its facile expression in a bacterial host. Here we show that HRP could be overexpressed as a soluble form by fusing the enzyme with Escherichia coli phosphoglycerate kinase (PGK). After simple incubation with calcium ion, hemin, and oxidized glutathione, PGK-HRP could be fully activated showing a higher molar specific activity than plant-derived HRP. Our established procedure did not use tedious and inefficient refolding steps that have been used to activate HRP produced as inclusion bodies and thus is superior in its overall yield (>72 mg purified HRP conjugate per L culture) to existing methods. By co-expressing PGK-HRP with ferrochelatase in a special host that permitted the formation of disulfide bonds in the cytoplasm, the activation steps could be simplified even though the resulting specific activity was low.