[Characterization of the affinity-tags-regulated (S)-carbonyl reductase 2 towards 2-hydroxyacetophenone reduction]

The influence of different affinity tags on enzyme characteristics varies. The (S)-carbonyl reductase 2 (SCR2) from Candida parapsilosis can reduce 2-hydroxyacetophenone, which is a valuable prochiral ketones. Different affinity tags, i.e. his-tag, strep-tag and MBP-tag, were attached to the N terminus of SCR2. These tagged SCR2 enzymes, i.e. his6-SCR2, strep-SCR2 and MBP-SCR2, were heterologously expressed in Escherichia coli and purified to study their characteristics towards 2-hydroxyacetophenone reduction. Affinity tags did affect the characteristics of the recombinant SCR2 enzymes. Specifically, affinity tags affect the stability of recombinant SCR2 enzymes: 1) At pH 6.0, the remaining enzyme activities of his6-SCR2 and strep-SCR2 were only 95.2% and 90.0% of the untagged SCR2, while that of MBP-SCR2 was 1.2 times of the untagged SCR2 after incubating for 13 h at 30 °C. 2) The half-life of MBP-SCR2 at 50 °C was 26.6%-48.8% longer than those of strep-SCR2, his6-SCR2 and untagged SCR2. 3) The kcat of MBP-SCR2 was about 1.25-1.45 times of that of small affinity-tagged and untagged SCR2 after storing at -80 °C for 60 d. Structural informatics indicated that the α-helices at the C terminus of MBP-SCR2 contributed to the stability of the N terminus of fusion protein of SCR2. Data from circular dichroism showed that the MBP-tag has some influence on the secondary structure of SCR2, while melting temperature analysis demonstrated that the Tm of the recombinant MBP-SCR2 was about 5 °C higher than that of the untagged SCR2. This study obtained an efficient and stable recombinant SCR2, i.e. the MBP-SCR2. Moreover, this study could serve as a reference for other researchers to evaluate and select appropriate affinity tags for their research.