Folding reporter tags can deliver misleading results upon chaperone coexpression

Chaperone coexpression is a common strategy for improving the folding quality of overexpressed proteins. Tags with quantifiable biological properties are often fused to the target protein as indicators of functional expression. Using a fusion of the enzymes AtCCD1 and GST, we show that chaperone coexpression can alter the folding quality of fusion protein moieties dissimilarly, sometimes even in opposite directions. Incorrect results can be obtained if target protein folding quality is assessed solely based on reporter tag activity. Thus, additional methods for the verification of the obtained results should be performed.