Ligand-based CoMFA and CoMSIA studies on chromone derivatives as radical scavengers

The antioxidant activity for a series of chromone compounds, evaluated by DPPH free radical scavenging assay, were subjected to 3D-QSAR studies using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). All 48 chromone derivatives were geometry optimized by AM1 and HF/6-31G^* calculations. The CoMFA and CoMSIA results were compared between different alignment strategies. The best CoMFA model obtained from HF/6-31G^* optimization with field fit alignment gave cross-validated r² (q²) = 0.821, noncross-validated r² = 0.987, S = 0.095, and F = 388.255. The best CoMSIA model derived from AM1 optimized structures and superimposition alignment gave q² = 0.876, noncross-validated r² = 0.976, S = 0.129, and F = 208.073, including electrostatic, hydrophobic, hydrogen bond donor and acceptor fields. The contour maps provide the fruitful structure–radical scavenging activity relationships which are useful for designing new compounds with higher activity.     

Engineered Si(1 0 0) surfaces for the gas-phase anchoring of metal β-diketonate complexes

A synthetic strategy for the covalent anchoring of nickel β-diketonate complexes on Si(1 0 0) has been examined. Engineered Si(1 0 0) surfaces were prepared by the Si-grafting of 10-undecylenic acid methyl ester followed by hydrolysis of the ester to free the carboxylic functions suited for the anchoring of the Ni complex. Bis(pentane-2,4-dionate)Ni(II) was bonded to the functionalized surface from the gas phase by the exchange of the acetylacetonate ligand with the grafted acid. The surface density of the anchored Ni complex was controlled by tuning the surface concentration of carboxylic groups adopting a mixed monolayer of undecylenic acid and 1-decene used as a spectator spacer. The nickel decorated silicon surfaces were characterized by attenuate total reflectance infrared absorption spectroscopy (ATR-IRAS) and angle resolved X-ray photoelectron spectroscopy (AR-XPS).     

Probing the catalytic mechanism of a C-3'-methyltransferase involved in the biosynthesis of D-tetronitrose

D ‐Tetronitrose is a nitro‐containing tetradeoxysugar found attached to the antitumor and antibacterial agent tetrocarcin A. The biosynthesis of this highly unusual sugar in Micromonospora chalcea requires 10 enzymes. The fifth step in the pathway involves the transfer of a methyl group from S‐adenosyl‐L ‐methionine (SAM) to the C‐3′ carbon of dTDP‐3‐amino‐2,3,6‐trideoxy‐4‐keto‐D ‐glucose. The enzyme responsible for this transformation is referred to as TcaB9. It is a monomeric enzyme with a molecular architecture based around three domains. The N‐terminal motif contains a binding site for a structural zinc ion. The middle‐ and C‐terminal domains serve to anchor the SAM and dTDP–sugar ligands, respectively, to the protein, and the active site of TcaB9 is wedged between these two regions. For this investigation, the roles of Tyr 76, His 181, Tyr 222, Glu 224, and His 225, which form the active site of TcaB9, were probed by site‐directed mutagenesis, kinetic analyses, and X‐ray structural studies. In addition, two ternary complexes of the enzyme with bound S‐adenosyl‐L ‐homocysteine and either dTDP‐3‐amino‐2,3,6‐trideoxy‐4‐keto‐D ‐glucose or dTDP‐3‐amino‐2,3,6‐trideoxy‐D ‐galactose were determined to 1.5 or 1.6 Å resolution, respectively. Taken together, these investigations highlight the important role of His 225 in methyl transfer. In addition, the structural data suggest that the methylation reaction occurs via retention of configuration about the C‐3′ carbon of the sugar.     

The regulation of mRNA stability in mammalian cells: 2.0

Messenger RNA decay is an essential step in gene expression to set mRNA abundance in the cytoplasm. The binding of proteins and/or noncoding RNAs to specific recognition sequences or secondary structures within mRNAs dictates mRNA decay rates by recruiting specific enzyme complexes that perform the destruction processes. Often, the cell coordinates the degradation or stabilization of functional subsets of mRNAs encoding proteins collectively required for a biological process. As well, extrinsic or intrinsic stimuli activate signal transduction pathways that modify the mRNA decay machinery with consequent effects on decay rates and mRNA abundance. This review is an update to our 2001 Gene review on mRNA stability in mammalian cells, and we survey the enormous progress made over the past decade.     

5-aza-CdR induces the demethylation of Syk promoter in nasopharyngeal carcinoma cell

The present study employed 5-aza-2′-deoxycytidine (5-aza-CdR) to treat nasopharyngeal carcinoma cell line CNE-1, CNE-2 and non-cancerous human nasopharyngeal epithelial cell line NP-69 to understand the effects on spleen tyrosine kinase (Syk) gene promoter methylation. The results showed that the methylation level of Syk gene is negatively associated with the differentiation level of the cell lines, and the 5-aza-CdR treatment decreased the methylation level in nasopharyngeal carcinoma cell lines. Additionally, the drug sensitivity of low-differentiated cell line was significantly higher than the high-differentiated cell line. In conclusion, the Syk gene promoter methylation reflects the cell differentiation status, and 5-aza-CdR treatment could induce the demethylation of Syk gene promoter.     

Human protein arginine methyltransferase 7 (PRMT7) is a type III enzyme forming ω-NG-monomethylated arginine residues

Full-length human protein arginine methyltransferase 7 (PRMT7) expressed as a fusion protein in Escherichia coli was initially found to generate only ω-N(G)-monomethylated arginine residues in small peptides, suggesting that it is a type III enzyme. A later study, however, characterized fusion proteins of PRMT7 expressed in bacterial and mammalian cells as a type II/type I enzyme, capable of producing symmetrically dimethylated arginine (type II activity) as well as small amounts of asymmetric dimethylarginine (type I activity). We have sought to clarify the enzymatic activity of human PRMT7. We analyzed the in vitro methylation products of a glutathione S-transferase (GST)-PRMT7 fusion protein with robust activity using a variety of arginine-containing synthetic peptides and protein substrates, including a GST fusion with the N-terminal domain of fibrillarin (GST-GAR), myelin basic protein, and recombinant human histones H2A, H2B, H3, and H4. Regardless of the methylation reaction conditions (incubation time, reaction volume, and substrate concentration), we found that PRMT7 only produces ω-N(G)-monomethylarginine with these substrates. In control experiments, we showed that mammalian GST-PRMT1 and Myc-PRMT5 were, unlike PRMT7, able to dimethylate both peptide P-SmD3 and SmB/D3 to give the expected asymmetric and symmetric products, respectively. These experiments show that PRMT7 is indeed a type III human methyltransferase capable of forming only ω-N(G)-monomethylarginine, not asymmetric ω-N(G),N(G)-dimethylarginine or symmetric ω-N(G),N(G')-dimethylarginine, under the conditions tested.     

A Type III restriction–modification system in Mycoplasma mycoides subsp. capri

The sequenced genome of Mycoplasma mycoides subsp. capri revealed the presence of a Type III restriction–modification system (MmyCI). The methyltransferase (modification) subunit of MmyCI (M.MmyCI) was shown to recognize the sequence 5′-TGAG-3′ and methylate the adenine. The coding region of the methyltransferase gene contains 12 consecutive AG dinucleotide repeats that result in a translational termination at a TAA codon immediately beyond the repeat region. This strain does not have MmyCI activity. A clone was found with 10 AG repeats such that the gene is in frame, and this strain has MmyCI activity, suggesting that the expression of the MmyCI methyltransferase may be phase variable.     

RNAi suppression of lignin biosynthesis in sugarcane reduces recalcitrance for biofuel production from lignocellulosic biomass

Sugarcane is a prime bioethanol feedstock. Currently, sugarcane ethanol is produced through fermentation of the sucrose, which can easily be extracted from stem internodes. Processes for production of biofuels from the abundant lignocellulosic sugarcane residues will boost the ethanol output from sugarcane per land area. However, unlocking the vast amount of chemical energy stored in plant cell walls remains expensive primarily because of the intrinsic recalcitrance of lignocellulosic biomass. We report here the successful reduction in lignification in sugarcane by RNA interference, despite the complex and highly polyploid genome of this interspecific hybrid. Down‐regulation of the sugarcane caffeic acid O‐methyltransferase (COMT) gene by 67% to 97% reduced the lignin content by 3.9% to 13.7%, respectively. The syringyl/guaiacyl ratio in the lignin was reduced from 1.47 in the wild type to values ranging between 1.27 and 0.79. The yields of directly fermentable glucose from lignocellulosic biomass increased up to 29% without pretreatment. After dilute acid pretreatment, the fermentable glucose yield increased up to 34%. These observations demonstrate that a moderate reduction in lignin (3.9% to 8.4%) can reduce the recalcitrance of sugarcane biomass without compromising plant performance under controlled environmental conditions.     

评估宫颈微浸润腺癌不同外科治疗的结果

目的:通过大样本的病例回顾,明确宫颈微浸润腺癌需要彻底外科治疗的病变范围。方法:46例因患宫颈微浸润腺癌(浸润深度小于或等于5mm)行外科手术治疗的病人,来自中国人民解放军总医院妇产科,同一位病理专家确定组织学类型、肿瘤分级、浸润深度、肿瘤宽度、有无淋巴管间的浸润、肿瘤边缘状况、宫旁状况以及是否有结节状的转移。病变分级参照FIGO(2009)的标准。结果:46例患者按照现行的FIGO分期标准,34例ⅠA1期,12例ⅠA2期。治疗方式主要有宫颈锥切、单纯全子宫切除、全子宫切除加淋巴结清扫、广泛子宫切除加淋巴结清扫。31例广泛全子宫切除的患者没有发现宫旁浸润。34例行淋巴结清扫的病人没有发现淋巴结转移。平均随访80个月未见复发。结论:关于微浸润腺癌的处理仍旧有争议,相对于微浸润宫颈鳞状细胞癌而言,传统的治疗宫颈微浸润腺癌彻底外科治疗更多一些。通过本次研究,我们认为宫颈为浸润癌基质浸润深度小于3mm或者FIGOIA1期的患者,简单的全子宫切除足够,不需要淋巴结清扫、广泛的子宫切除和卵巢切除。