A fusion protein strategy for soluble expression of glycosyltransferase UGT76G1 in .

The UDP-glucosyltransferase UGT76G1 from converts stevioside to rebaudioside A via a one-step glycosylation reaction， which increases the amount of sweet-tasting rebaudioside A and decreases the amount of stevioside that has a bitter aftertaste. This enzyme could， therefore， conceivably be used to improve the organoleptic properties of steviol glycosides and offer a cost-effective preparation of high-purity rebaudioside A. Producing soluble enzymes by overexpression is a prerequisite for large-scale biocatalysis. However， most of the UGT76G1 overexpressed in is in inclusion bodies. In this study， three N-terminal fusion partners， 3'-phosphoadenosine-5'-phosphatase (CysQ)， 2-keto-3-deoxy-6-phosphogluconate aldolase (EDA) and N-utilisation substance A (NusA)， were tested to improve UGT76G1 expression and solubility in . Compared with the fusion-free protein， the solubility of UGT76G1 was increased 40% by fusion with CysQ， and the glucosyltransferase activity of the crude extract was increased 82%. This successful CysQ fusion strategy could be applied to enhance the expression and solubility of other plant-derived glucosyltransferases and presumably other unrelated proteins in the popular， convenient and cost-effective host.