1,5-Anhydro- -fructose: regioselective acylation with fatty acids

Regioselective acylation of 1,5-anhydro- -fructose was performed with dodecanoic acid to give 1,5-anhydro-6-O-dodecanoyl- -fructose, chemically in 50% yield and enzymatically in quantitative yield. Quantitative conversions were also obtained using hexadecanoic and octadecanoic acids as acyl donors.     

Raising the list of SirT7 targets to a new level

Sirtuins are crucial proteins involved in sensing and coordinating the response to different forms of stress, mainly through NAD⁺‐dependent deacetylation of proteins. For that reason, sirtuins are directly involved in many human pathologies including cancer, diabetes, cardiovascular and neurodegenerative diseases. SirT7, one of the less well‐understood sirtuins, has been associated with ribosome biogenesis, gene expression, metabolism and cancer. Despite the wide range of these functions, only a handful of targets for SirT7 have so far been described. In this issue, Zhang et al. report the first proteomic screening of SirT7 substrates. Using stable isotope labeling with amino acids in cell culture (SILAC), coupled with quantitative mass spectrometry, they have identified a comprehensive list of candidates involved in a variety of functions, ranging from maintenance of chromatin architecture to gene silencing and metabolism. A selected group of these candidates has been validated by in vitro co‐immunoprecipitation and deacetylation experiments. Predictive tools have identified additional candidates. The identification of these novel targets not only suggests new ways of understanding the physiological role of SirT7, but also provides new evidence to add to our existing knowledge of the global impact of sirtuins in cell homeostasis.     

Histone deacetylation directs DNA methylation in survivin gene silencing

DNA methylation and histone acetylation are major epigenetic modifications in gene silencing. In our previous research, we found that the methylated oligonucleotide (SurKex) complementary to a region of promoter of survivin could induce DNA methylation in a site-specific manner leading to survivin silencing. Here, we further studied the role of histone acetylation in survivin silencing and the relationship between histone acetylation and DNA methylation.First we observed the levels of histone H4 and H4K16 acetylation that were decreased after SurKex treatment by using the chromatin immunoprecipitation (ChIP) assay. Next, we investigated the roles of histone acetylation and DNA methylation in survivin silencing after blockade of histone deacetylation with Trichostatin A (TSA). We assessed survivin mRNA expression by RT-PCR, measured survivin promoter methylation by bisulfite sequencing and examined the level of histone acetylation by the ChIP assay. The results showed that histone deacetylation blocked by TSA reversed the effects of SurKex on inhibiting the expression of survivin mRNA, inducing a site-specific methylation on survivin promoter and decreasing the level of histone acetylation. Finally, we examined the role of histone acetylation in the expression of DNA methyltransferase 1 (DNMT1) mRNA. The results showed that histone deacetylation blocked by TSA reversed the increasing effect of histone deacetylation on the expression of survivin mRNA. This study suggests that histone deacetylation guides SurKex-induced DNA methylation in survivin silencing possibly through increasing the expression of DNMT1 mRNA.     

微波法制备壳聚糖研究

采用微波炉加热,在敞口容器中,进行甲壳素脱乙酰反应,制备壳聚糖。考察了碱溶液浓度和微波加热时间对壳聚糖脱乙酰度的影响。固定微波加热时间30min,随NaOH溶液浓度增加,脱乙酰度先增加,后减小;NaOH溶液浓度为45％时,壳聚糖的脱乙酰度最高。固定NaOH溶液浓度为45％,随着微波加热时间延长,壳聚糖的脱乙酰度增加。微波加热的最佳时间为30min。加热时间继续延长,壳聚糖变黑。碱溶液浓度和微波加热时间对壳聚糖的粘均分子量影响都不大。本文试图从微波场的能量分布和微波加热机理方面解释实验结果。     

Possible regulation of Toll-like receptor 4 by lysine acetylation through LPCAT2 activity in RAW264.7 cells

Inflammation is central to several diseases. TLR4 mediates inflammation by recognising and binding to bacterial lipopolysaccharides and interacting with other proteins in the TLR4 signalling pathway. Although there is extensive research on TLR4-mediated inflammation, there are gaps in understanding its mechanisms. Recently, TLR4 co-localised with LPCAT2, a lysophospholipid acetyltransferase. LPCAT2 is already known to influence lipopolysaccharide-induced inflammation; however, the mechanism of LPCAT2 influencing lipopolysaccharide-mediated inflammation is not understood.The present study combined computational analysis with biochemical analysis to investigate the influence of LPCAT2 on lysine acetylation in LPS-treated RAW264.7 cells.The results suggest for the first time that LPCAT2 influences lysine acetylation in LPS-treated RAW264.7 cells. Moreover, we detected acetylated lysine residues on TLR4. The present study lays a foundation for further research on the role of lysine acetylation on TLR4 signalling. Moreover, further research is required to characterise LPCAT2 as a protein acetyltransferase.     

细菌体内乙酰化修饰研究进展

翻译后修饰是指前体蛋白经过一系列加工修饰形成具有多种功能的蛋白质,其可以发生在不同的氨基酸侧链或肽键上,通常是由酶活性介导的.5％的蛋白质组组成的酶介导了超过200多种的翻译后修饰类型,其中乙酰化修饰是一种重要的翻译后修饰途径.乙酰化修饰在真核细胞中被广泛研究,其几乎参与细胞的所有生理活动并且高度保守.最近的很多研究表...     

Short chain regioselectively hydrolyzed scleroglucans induce maturation of porcine dendritic cells

Branched β-1,3/1,6-glucans (scleroglucan) were produced by cultivation of Sclerotium rolfsii ATCC 15205. Regioselective hydrolysis at the β-1,3-linkage of the cell-free and purified polysaccharide was performed in borosilicate glass bottles at pH 5, 121°C, and 1 bar for 72 h. The mixture was divided into four molar mass fractions by stepwise cross-flow filtration using different cutoffs. In vitro studies revealed that scleroglucan hydrolysates with a low molar mass of less than 5 kDa significantly stimulated the activation and maturation of porcine monocyte derived dendritic cells (MoDC) by upregulation of CD40 and CD80/86 as well as by reduction of antigen uptake. MoDC treated with low molar mass scleroglucan showed a considerable increase in the amounts of secreted proinflammatory cytokine tumor necrosis factor alpha and stimulated the proliferation of lymphocytes. Therefore, scleroglucan molecules of low molecular weight are able to induce activation and maturation of porcine DC, which are key initiators of inflammatory and adaptive immune responses, and could provide improved protection against infectious diseases.     

Acs is essential for propionate utilization in Escherichia coli

Bacteria like Escherichia coli can use propionate as sole carbon and energy source. All pathways for degradation of propionate start with propionyl-CoA. However, pathways of propionyl-CoA synthesis from propionate and their regulation mechanisms have not been carefully examined in E. coli. In this study, roles of the acetyl-CoA synthetase encoding gene acs and the NAD⁺-dependent protein deacetylase encoding gene cobB on propionate utilization in E. coli were investigated. Results from biochemical analysis showed that, reversible acetylation also modulates the propionyl-CoA synthetase activity of Acs. Subsequent genetic analysis revealed that, deletion of acs in E. coli results in blockage of propionate utilization, suggesting that acs is essential for propionate utilization in E. coli. Besides, deletion of cobB in E. coli also results in growth defect, but only under lower concentrations of propionate (5 mM and 10 mM propionate), suggesting the existence of other propionyl-CoA synthesis pathways. In combination with previous observations, our data implies that, for propionate utilization in E. coli, a primary amount of propionyl-CoA seems to be required, which is synthesized by Acs.