ABSTRACT
C-Glycosides are important natural products with various bioactivities. In plant biosynthetic pathways, the C-glycosylation step is usually catalyzed by C-glycosyltransferases (CGTs), and most of them prefer to accept uridine 5'-diphosphate glucose (UDP-Glc) as sugar donor. No CGTs favoring UDP-rhamnose (UDP-Rha) as sugar donor has been reported, thus far. Herein, we report the first selective C-rhamnosyltransferase VtCGTc from the medicinal plant Viola tricolor. VtCGTc could efficiently catalyze C-rhamnosylation of 2-hydroxynaringenin 3-C-glucoside, and exhibited high selectivity towards UDP-Rha. Mechanisms for the sugar donor selectivity of VtCGTc were investigated by molecular dynamics (MD) simulations and molecular mechanics with generalized Born and surface area solvation (MM/GBSA) binding free energy calculations. Val144 played a vital role in recognizing UDP-Rha, and the V144T mutant could efficiently utilize UDP-Glc. This work provides a new and efficient approach to prepare flavonoid C-rhamnosides such as violanthin and iso-violanthin.
ABSTRACT
Huang-Qin is a traditional Chinese medicine with antiviral, antioxidant, and anti-inflammatory activities. Its major bioactive compounds are diverse flavone O-glucuronides and glucosides. Although three flavonoid O-glycosyltransferases have been identified from S. baicalensis, this information is not sufficient to elucidate the structural diversity of flavonoid glycosides. In this study, nine glycosyltransferase candidate genes were discovered from S. baicalensis by BLAST analysis and their functions were characterized after heterologous expression. Three new flavone O-glycosyltransferases were able to catalyze the formation of major compounds in S. baicalensis, including baicalin and wogonoside. These enzymes could also utilize exogenous flavones as sugar acceptors. This work further elucidates biosynthetic pathways for Scutellaria flavonoid O-glycosides.
ABSTRACT
<p><b>OBJECTIVE</b>To investigate the clinical significance of matrix metalloproteinase-9 (MMP-9) and tissue factor (TF) secreted by cultured monocyte-derived macrophages (HMDM) from patients with coronary heart disease (CHD) in vitro, and to evaluate the intervenient effect of puerarin (Pur) on them.</p><p><b>METHODS</b>A total of 40 patients were enrolled, including 12 patients with acute myocardial infarction (AMI), 16 patients with unstable angina pectoris (UAP), 12 patients with stable angina pectoris (SAP). Besides, 8 healthy subjects with normal coronary arteriograph were set as controls. Monocytes acquired from their peripheral blood were incubated for 48 h and induced to differentiate into macrophages by phorbolester 12-myristate 13-acetate (PMA), the contents of MMP-9 and TF in supernatant were assayed, and the relationship of them with patients' age, risk factors of CHD and coronary artery lesion scores were analyzed. HMDMs randomly from selected 12 patients with acute coronary syndrome (ACS) were arranged for observing the intervenient effects of different concentrations of Pur on the levels and activity of MMP-9 and TF.</p><p><b>RESULTS</b>The levels of MMP-9 and TF in UAP and AMI patients were significantly higher than those in SAP patients and healthy subjects (P < 0.01), but no statistical correlation was found between levels of MMP-9 and TF with different CHD risk factors, as well as patients' age and coronary artery lesion scores. The levels and activity of MMP-9 and TF in the 12 ACS patients were significantly decreased in a dose-dependent manner after Pur intervention when compared with the controt group.</p><p><b>CONCLUSION</b>The levels of MMP-9 and TF secreted in vitro by HMDM from CHD patients could be taken as indexes for evaluating patient's condition of ACS. Pur can inhibit the expression and the activity of MMP-9 and TF secreted by HMDM, stabilize the plaque and improve the vulnerability of blood to certain extent.</p>