RESUMEN
Objective: To study the chemical constituents from the aerial parts of Scoparia dulcis. Methods: Various chromatographic techniques were used to separate the constituents and their structures were elucidated using spectroscopic methods and by comparing their data to those reported in the literatures. The α-glucosidase inhibitory activity assay was used to identify potential α-glucosidase inhibitors. Results: Nine compounds were isolated from the aerial parts of S. dulcis. Their structures were identified as Scoparic zolone (1), (2S)-2,7-dihydroxy-2H-1,4-benzoxazin-3(4H)-one (2), (2R)-7-hydroxy-2H-1,4-benzoxazin-3(4H)-one-2-O-ß-d-glucopyranoside (3), (2R)-7-methoxy-2H-1,4-benzoxazin-3(4H)-one-2-O-ß-d-glucopyranoside (4), (2S)-7-hydroxy-2H-1,4-benzoxazin-3(4H)-one-2-O-ß-d-glucopyranoside (5), 6-methoxy-benzoxazolin-2(3H)-one (6), 4-acetonyl-3,5-dimethoxy-p-quinol (7), zizyvoside I (8), and 3,4-dihydroxy benzeneacetic acid (9). Compound 2 showed the potent α-glucosidase inhibitory activity with an IC50 value of (132.8 ± 11.5) µmol/L, which is 28-fold higher than the positive control acarbose. Conclusion: Compound 1 is a new natural product. Compounds 2 and 9 have not been reported in Scoparia before. Compounds 3, 5, 7, 8 are isolated from Scrophulariaceae for the first time.
RESUMEN
Cofactors are crucial for the biosynthesis of natural compounds, and cofactor engineering is a useful strategy for enzyme optimization due to its potential to enhance enzyme efficiency. Secoisolariciresinol dehydrogenase (SIRD) was reported to convert secoisolariciresinol into matairesinol in an NAD+-dependent reaction. Here, a SIRD designated as IiSIRD2 identified from Isatis indigotica was found to utilize NADP+ as the cofactor. To explore the structural basis for this unique cofactor preference, model-based structural analysis was carried out, and it was postulated that a variation at the GXGGXG glycine-rich motif of IiSIRD2 alters its cofactor preference. This study paves way for future investigations on SIRD cofactor specificity and cofactor engineering to improve SIRD's catalytic efficiency.
RESUMEN
Understanding the mechanisms of enzyme specificity is increasingly important from a fundamental viewpoint and for practical applications. Transglycosylation has attracted many attentions due to its importance in improving the functional properties of acceptor substrates both in vivo and in vitro. Cyclodextrin glucanotransferase (CGTase) is one of the key enzymes in transglycosylation, it has a broad substrate spectrum and utilizes sugar as the donor. However, little is known about the acceptor selectivity of CGTase, which greatly hampers efforts toward the rational design of desirable transglycosylated derivatives. In this study, we found that the CGTase from Bacillus circulans, BcCGTase, was able to form glycosylated products with diverse ginsenosides. In particular, it not only carries out diverse mono-, di-, and even higher-order glycosylations via the transfer of glucose moieties to the COGlc positions, but also can glycosylate the C3-OH position of ginsenosides. In contrast, another CGTase from Bacillus licheniformis (BlCGTase) showed relatively specific acceptor preference with only several ginsenosides. Structural comparison between BcCGTase and BlCGTase revealed that the Arg74/K81 position within the acceptor-binding sites of BcCGTase/BlCGTase was responsible for the differences in catalytic specificity for ginsenoside F1. Further mutagenesis confirmed their roles in the acceptor selection. In conclusion, our study not only demonstrates the acceptor selectivity of CGTases, but also provides insight into the catalytic mechanism of CGTases, which will potentially increase the utility of CGTase for biosynthesis of new, rationally designed transglycosylated derivatives.
