CdpNPT, an N-prenyltransferase from Aspergillus fumigatus: overproduction, purification and biochemical characterisation

A putative prenyltransferase gene, cdpNPT, was identified in the genome sequence of Aspergillus fumigatus by a homology search by using known prenyltransferases and sequence analysis. CdpNPT consists of 440 amino acids and has a molecular mass of about 50 kDa. The coding sequence of cdpNPT was cloned in pQE60 and overexpressed in E. coli. The soluble His(6)-fusion CdpNPT was purified to near homogeneity and characterised biochemically. The enzyme showed broad substrate specificity towards aromatic substrates and was found to catalyse the prenylation of tryptophan-containing cyclic dipeptides at N1 of the indole moieties in the presence of dimethylallyl diphosphate (DMAPP); geranyl diphosphate was not accepted as prenyl donor. The structures of the enzymatic products were elucidated by NMR and MS analysis. The K(m) value for DMAPP was determined to be 650 microM. Due to substrate inhibition, K(m) values could not be obtained for the aromatic substrates. CdpNPT does not need divalent metal ions for its enzymatic reaction, although Ca(2+) enhances the reaction velocity by up to the threefold. CdpNPT is the first N-prenyltransferase that has been purified and characterised in a homogenous form after heterologous overproduction. Interestingly, it shows significant sequence similarity to other indole prenyltransferases that catalyse the formation of C--C bonds.     

Metabolic footprinting as a tool for discriminating between brewing yeasts

The characterization of industrial yeast strains by examining their metabolic footprints (exometabolomes) was investigated and compared to genome-based discriminatory methods. A group of nine industrial brewing yeasts was studied by comparing their metabolic footprints, genetic fingerprints and comparative genomic hybridization profiles. Metabolic footprinting was carried out by both direct injection mass spectrometry (DIMS) and gas chromatography time-of-flight mass spectrometry (GC-TOF-MS), with data analysed by principal components analysis (PCA) and canonical variates analysis (CVA). The genomic profiles of the nine yeasts were compared by PCR-restriction fragment length polymorphism (PCR-RFLP) analysis, genetic fingerprinting using amplified fragment length polymorphism (AFLP) analysis and microarray comparative genome hybridizations (CGH). Metabolomic and genomic analysis comparison of the nine brewing yeasts identified metabolomics as a powerful tool in separating genotypically and phenotypically similar strains. For some strains discrimination not achieved genomically was observed metabolomically.     

Mononuclear Cu-O2 complexes: geometries, spectroscopic properties, electronic structures, and reactivity

Using interwoven experimental and theoretical methods, detailed studies of several structurally defined 1:1 Cu-O 2 complexes have provided important fundamental chemical information useful for understanding the nature of intermediates involved in aerobic oxidations in synthetic and enzymatic copper-mediated catalysis. In particular, these studies have shed new light on the factors that influence the mode of O 2 coordination (end-on vs side-on) and the electronic structure, which can vary between Cu(II)-superoxo and Cu(III)-peroxo extremes.     

Shape dependence of band-edge exciton fine structure in CdSe nanocrystals

The band-edge exciton fine structure of wurtzite CdSe nanocrystals is investigated by a plane-wave pseudopotential method that includes spin-orbit coupling, screened electron-hole Coulomb interactions, and exchange interactions. Large-scale, systematic simulations have been carried out on quantum dots, nanorods, nanowires, and nanodisks. The size and shape dependence of the exciton fine structure is explored over the whole diameter-length configuration space and is explained by the interplay of quantum confinement, intrinsic crystal-field splitting, and electron-hole exchange interactions. Our results show that the band-edge exciton fine structure of CdSe nanocrystals is determined by the origin of their valence-band single-particle wave functions. Nanocrystals where the valence-band maximum originates from the bulk A band have a "dark" ground-state exciton. Nanocrystals where the valence-band maximum is derived from the bulk B band have a "quasi-bright" ground-state exciton. Thus, the diameter-length configuration map can be divided into two regions, corresponding to dark and quasi-bright ground-state excitons. We find that the dark/quasi-bright ground-state exciton crossover is not only diameter-dependent but also length-dependent, and it is characterized by a curve in the two-parameter space of diameter and length.     

Multi-functional chitosan nanoparticles encapsulating quantum dots and Gd-DTPA as imaging probes for bio-applications

Chitosan was used to encapsulate both CdSe/ZnS quantum dots (QDs) and the magnetic resonance imaging (MRI) contrast agent gadolinium-diethylenetriaminepentaacetate (Gd-DTPA), forming multi-functional nanoparticles that can be used in a wide range of in vitro or in vivo studies as fluorescent biological labels as well as MRI contrast agents, respectively. Multi-color QDs at pre-determined molar ratios were encapsulated into chitosan nanoparticles to produce bar-coding fluorescent labels. The encapsulated QDs and Gd-DTPA still maintained their desirable optical properties and relatively high relaxivity, respectively. The chitosan nanoparticles also showed good aqueous stability and enhanced biocompatibility on myoblast cells.     

食品中赭曲霉毒素A检测方法研究进展

赭曲霉毒素A(ochratoxin A, OTA)是曲霉属和青霉属等有毒真菌产生的一类次级代谢产物,是常见污染食品的五大真菌毒素之一,具有较强的肾毒性、肝毒性、神经毒性和免疫毒性,以及致畸、致癌和致突变作用。OTA广泛存在于各种谷物及其制品、葡萄与葡萄酒、咖啡等多种食品原料及其成品中,严重威胁人体健康,因此有必要建立快速、准确、灵敏的OTA检测方法。针对食品中OTA的检测,目前已经拥有许多方法,如薄层色谱法,高效液相色谱法,液相-质谱联用法以及酶联免疫吸附法等。本研究对赭曲霉毒素A不同检测方法的原理、优缺点等进行归纳总结,旨在为食品中OTA的检测提供支持。     

黑果腺肋花楸多酚的抑菌活性研究

研究黑果腺肋花楸多酚对5种细菌和2种真菌的抑菌活性及其抑菌稳定性。采用双层平板打孔法,根据抑菌圈直径判断黑果腺肋花楸多酚的抑菌活性;采用比色法测定黑果腺肋花楸多酚对5种细菌的最小抑菌浓度(minimum inhibitory concentration,MIC),并以脂环酸芽孢杆菌和枯草芽孢杆菌作为指示菌,研究Na Cl浓度、温度、紫外线对黑果腺肋花楸多酚抑菌稳定性的影响。研究结果表明黑果腺肋花楸多酚对脂环酸芽孢杆菌、枯草芽孢杆菌等5种细菌均具有较好的抑菌活性,对2种真菌基本无抑菌效果。黑果腺肋花楸多酚对脂环酸芽孢杆菌(DSM 3922,AAT-92)、阴沟肠杆菌(20051)的MIC为0.40 g/L,对枯草芽孢杆菌(10034)和产气肠杆菌(10017)的MIC分别为0.05 g/L和0.10 g/L。随着Na Cl浓度的增加,黑果腺肋花楸多酚抑菌活性显著下降。多酚溶液经热处理后,抑菌活性有微弱下降趋势,经紫外线处理后抑菌活性基本无变化。     

Ta2O5-Incorporated WO3 nanocomposite film for improved electrochromic performance in an acidic condition

We report electrochromic and electrochemical properties of a WO3-Ta2O5 nanocomposite electrode that was fabricated from co-sputtering. Transmission electron microscopy (TEM) images of the WO3-Ta20 nanocomposite electrode revealed that morphology of the WO3 film was changed by incorporation of Ta2O5 nanoparticles, and their chemical states were confirmed to be W6+ and Ta5+ oxides from X-ray photoelectron spectroscopy (XPS). The introduction of Ta2O5 to the WO3 film played a role in alleviating surface roughness increase during continuous potential cycling; whereas the surface roughness of the WO3 film was increased from ca. 3.0 nm to ca. 13.4 nm after 400 cycles, the roughness increase on the WO3-Ta2O5 was significantly reduced to 4.2 nm after 400 cycles, as investigated by atomic force microscopy (AFM). This improvement of the stability by adding Ta2O5 may be responsible for the enhanced electrochemical and optical properties over long-term cycling with the WO3-Ta2O5 nanocomposite electrode.