Alternative application of an affinity purification tag: hexahistidines in ester hydrolysis

Hexahistidines are very common tags used in the affinity chromatography purification of recombinant proteins. Although these tags are solely applied for their metal-binding properties, we found that they are also able to perform ester hydrolysis when attached to a protein. For instance, green fluorescent protein (GFP) and the cowpea chlorotic mottle virus (CCMV) are able to perform catalysis after introduction of the His-tag. By attaching a His-tag to an enzyme, a dual-functional catalyst was created, that can perform a two-step cascade reaction. These findings show that the catalytic properties of the hexahistidine tag should be taken into consideration when choosing a suitable protein purification tag.