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Anthraquinone and its derivatives show remarkable biological properties such as anticancer, antibacterial, antifungal, and antiviral activities. Hence, anthraquinones derivatives have been of prime interest in drug development. This study developed a recombinant Escherichia coli strain to modify chrysazin to chrysazin-8-O-α-l-rhamnoside (CR) and chrysazin-8-O-α-l-2′-O-methylrhamnoside (CRM) using rhamnosyl transferase and sugar-O-methyltransferase. Biosynthesized CR and CRM were structurally characterized using HPLC, high-resolution mass spectrometry, and various nuclear magnetic resonance analyses. Antimicrobial effects of chrysazin, CR, and CRM against 18 superbugs, including 14 Gram-positive and 4 Gram-negative pathogens, were investigated. CR and CRM exhibited antimicrobial activities against nine pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA) in a disk diffusion assay at a concentration of 40 µg per disk. There were MIC and MBC values of 7.81–31.25 µg/mL for CR and CRM against methicillin-sensitive S. aureus CCARM 0205 (MSSA) for which the parent chrysazin is more than >1000 µg/mL. Furthermore, the anti-proliferative properties of chrysazin, CR, and CRM were assayed using AGS, Huh7, HL60, and HaCaT cell lines. CR and CRM showed higher antibacterial and anticancer properties than chrysazin. [ABSTRACT FROM AUTHOR]

Rhamnose-associated molecules are attracting attention because they are present in bacteria but not mammals, making them potentially useful as antibacterial agents. Additionally, they are also valuable for tumor immunotherapy. Thus, studies on the functions and biosynthetic pathways of rhamnose-containing compounds are in progress. In this paper, studies on the biosynthetic pathways of three rhamnose donors, i.e., deoxythymidinediphosphate-L-rhamnose (dTDP-Rha), uridine diphosphate-rhamnose (UDP-Rha), and guanosine diphosphate rhamnose (GDP-Rha), are firstly reviewed, together with the functions and crystal structures of those associated enzymes. Among them, dTDP-Rha is the most common rhamnose donor, and four enzymes, including glucose-1-phosphate thymidylyltransferase RmlA, dTDP-Glc-4,6-dehydratase RmlB, dTDP-4-keto-6-deoxy-Glc-3,5-epimerase RmlC, and dTDP-4-keto-Rha reductase RmlD, are involved in its biosynthesis. Secondly, several known rhamnosyltransferases from Geobacillus stearothermophilus, Saccharopolyspora spinosa, Mycobacterium tuberculosis, Pseudomonas aeruginosa, and Streptococcus pneumoniae are discussed. In these studies, however, the functions of rhamnosyltransferases were verified by employing gene knockout and radiolabeled substrates, which were almost impossible to obtain and characterize the products of enzymatic reactions. Finally, the application of rhamnose-containing compounds in disease treatments is briefly described. [ABSTRACT FROM AUTHOR]

The fungal cell wall is an attractive structure to look for new antifungal drug targets and for understanding the host-fungus interaction. Sporothrix schenckii is one of the main causative agents of both human and animal sporotrichosis and currently is the species most studied of the Sporothrix genus. The cell wall of this organism has been previously analyzed, and rhamnoconjugates are signature molecules found on the surface of both mycelia and yeast-like cells. Similar to other reactions where sugars are covalently linked to other sugars, lipids, or proteins, the rhamnosylation process in this organism is expected to involve glycosyltransferases with the ability to transfer rhamnose from a sugar donor to the acceptor molecule, i.e., rhamnosyltransferases. However, no obvious rhamnosyltransferase has thus far been identified within the S. schenckii proteome or genome. Here, using a Hidden Markov Model profile strategy, we found within the S. schenckii genome five putative genes encoding for rhamnosyltransferases. Expression analyses indicated that only two of them, named RHT1 and RHT2, were significantly expressed in yeast-like cells and during interaction with the host. These two genes were heterologously expressed in Escherichia coli, and the purified recombinant proteins showed rhamnosyltransferase activity, dependent on the presence of UDP-rhamnose as a sugar donor. To the best of our knowledge, this is the first report about rhamnosyltransferases in S. schenckii. [ABSTRACT FROM AUTHOR]

Isorhamnetin-3-O-rhamnoside was synthesized by a highly efficient three-enzyme (rhamnosyltransferase, glycine max sucrose synthase and uridine diphosphate (UDP)-rhamnose synthase) cascade using a UDP-rhamnose regeneration system. The rhamnosyltransferase gene (78D1) from Arabidopsis thaliana was cloned, expressed, and characterized in Escherichia coli. The optimal activity was at pH 7.0 and 45 °C. The enzyme was stable over the pH range of 6.5 to 8.5 and had a 1.5-h half-life at 45 °C. The Vmax and Km for isorhamnetin were 0.646 U/mg and 181 μM, respectively. The optimal pH and temperature for synergistic catalysis were 7.5 and 25 °C, and the optimal concentration of substrates were assayed, respectively. The highest titer of isorhamnetin-3-O-rhamnoside production reached 231 mg/L with a corresponding molar conversion of 100%. Isorhamnetin-3-O-rhamnoside was purified and the cytotoxicity against HepG2, MCF-7, and A549 cells were evaluated. Therefore, an efficient method for isorhamnetin-3-O-rhamnoside production described herein could be widely used for the rhamnosylation of flavonoids. [ABSTRACT FROM AUTHOR]