Sensitivity and specificity amplification in signal transduction

Intracellular signal transduction pathways transmit signals from the cell surface to various intracellular destinations, such as cytoskeleton and nucleus through a cascade of protein-protein interactions and activation events, leading to phenotypic changes such as cell proliferation, differentiation, and death. Over the past two decades, numerous signaling proteins and signal transduction pathways have been discovered and characterized. There are two major classes of signaling proteins: phosphoproteins (e.g., mitogen-activated protein kinases) and guanosine triphosphatases (GTPases; e.g., Ras and G proteins). They both function as molecular switches by addition and removal of one or more high-energy phosphate groups. This review discusses developments that seek to quantify the signal transduction processes with kinetic analysis and mathematical modeling of the signaling phosphoproteins and GTPases. These studies have provided insights into the sensitivity and specificity amplification of biological signals in integrated systems.     

大曲来源淀粉利用型乳酸菌的筛选及其淀粉利用特性

【背景】乳酸菌是面包、馒头等发酵食品中的重要功能微生物,对改善质地和风味均具有重要作用。淀粉利用能力高的乳酸菌,因其能够在生面粉中更好地定殖而具有重要的应用价值。【目的】筛选获得淀粉水解型乳酸菌并研究其淀粉利用特性。【方法】以浓香型白酒大曲为筛选源,采用淀粉基质碳源对大曲中乳酸菌进行定向富集,结合淀粉发酵能力筛选高淀粉利用能力菌株,并对筛选得到的优良菌株展开淀粉酶表达及其酶活力研究。【结果】以贮存3-6个月的大曲为优秀筛选源,以生面糊传代富集方法可较快筛选出具有良好淀粉利用能力的乳杆菌,主要物种为植物乳杆菌和类食品乳杆菌。对其中一株具有淀粉利用能力的类食品乳杆菌LBM12001的淀粉水解特征和淀粉酶活力展开研究,该菌株淀粉水解能力达10 g/L,并且其在面糊中具有良好的定殖能力;酶活力测定表明,其α-淀粉酶和麦芽糖淀粉酶为胞外酶;麦芽糖淀粉酶水解淀粉的最适pH值为3.5,比酶活为1 240 U/mg。【结论】建立起从我国传统白酒发酵大曲中高效筛选淀粉水解型乳酸菌的富集筛选方法,以及菌株的水解能力评价方法,获得的胞外麦芽糖淀粉酶分泌型乳杆菌在酸面团、馒头等需进行生面粉发酵食品的生产中具有重要应用前景。     

长角血蜱唾液腺中腺苷三磷酸双磷酸酶的纯化及其酶切机制

利用染料亲和层析(Cibacorn Blue柱)和离子交换层析(Macrosphere WCX柱)对长角血蜱Haemaphysalis longicornis唾液腺的腺苷三磷酸双磷酸酶进行纯化,经SDS-PAGE证实其分子量为66 kD。腺苷三磷酸双磷酸酶可以水解ATP和ADP,但对AMP无水解作用,水解ATP和ADP的K_m值均为0.2 μmol/L,V_max值分别为12.5和15.6 μmol/(min·mg)。腺苷三磷酸双磷酸酶水解ATP的中间产物是ADP,最终产物是AMP和正磷酸。表明腺苷三磷酸双磷酸酶水解ATP的位点是5'-核苷酸的γ-磷酸键,水解ADP的位点是5'-核苷酸的β-磷酸键。     

Formation of α- and β-conidia by Phaeocytostroma ambiguum

The formation of conidia in Phaeocytostroma ambiguum on different media and conditions was investigated in this study. Carnation leaf agar (CLA) and a 12 h photoperiod (24/18 °C) provided excellent conditions for the promotion of rapid formation of both alpha (α) and beta (β) conidia in a number of P. ambiguum isolates. The dimensions of α- and β-conidia amounted to 6.0–19.6 × 3.8–7.5 μm and 6.0–24.9 × 1.1–2.6 μm, respectively. They were produced on short or elongate, simple and branched conidiophores. β-conidia have not been described before in P. ambiguum. Intermediate conidia were rarely found. This revised version was published online in August 2006 with corrections to the Cover Date.     

An update on enzymatic cocktails for lignocellulose breakdown

Alternative energy sources have received increasing attention in recent years. The possibility of adding value to agricultural wastes, by producing biofuels and other products with economic value from lignocellulosic biomass by enzymatic hydrolysis, has been widely explored. Lignocellulosic biomass, as well as being an abundant residue, is a complex recalcitrant structure that requires a consortium of enzymes for its complete degradation. Pools of enzymes with different specificities acting together usually produce an increase in hydrolysis yield. Enzymatic cocktails have been widely studied due to their potential industrial application for the bioconversion of lignocellulosic biomass. This review presents an overview of enzymes required to degrade the plant cell wall, paying particular attention to the latest advances in enzymatic cocktail production and the main results obtained with cocktails used to degrade a variety of types of biomass, as well as some future perspectives within this field.     

Fusarium pallidoroseum L. on castor (Ricinus communis) in Samaru,Nigeria

Diseased castor leaves were collected from the Institute for Agricultural Research (IAR) fields and taken to the laboratory for isolation. Leaves were grown on Potato Dextrose Agar with Streptomycin and incubated for seven days. Grown cultures were observed under microscope and Fusarium pallidoroseum was isolated as confirmed by IMI. Inoculated leaves showed symptoms of wilts and blight.     

Development of efficient one-pot three-component assembly of trityl olmesartan medoxomil

We have elaborated a one-pot three-component assembly of trityl olmesartan medoxomil starting from commercially available ethyl 4-(2-hydroxypropan-2-yl)-2-propyl-1H-imidazole-5-carboxylate, 5-(4′-(bromomethyl)-[1,1′-biphenyl]-2-yl)-1-trityl-1H-tetrazole and 4-(chloromethyl)-5-methyl-1,3-dioxol-2-one intermediates. The developed and optimized one-pot process provides 72–75% yield of trityl olmesartan medoxomil over three steps, which represents in average ca. 90% yield per synthetic step, on a 300?g scale. The process is conducted in simple fashion and provides highly pure trityl olmesartan medoxomil (up to 97.5% by HPLC), which can be easily converted to olmesartan medoxomil that fully complies with all ICH requirements. Furthermore, the described process significantly improves the primary process to trityl olmesartan medoxomil by drastic reduction of required unit operations and application of single reaction solvent through the reaction sequence. Moreover, the amount of used organic solvents was notably reduced. The developed process has provided solid bases for industrial production of trityl olmesartan medoxomil.     

Review. ATP hydrolysis-driven gating in cystic fibrosis transmembrane conductance regulator

Proteins belonging to the ATP-binding cassette superfamily couple ATP binding and hydrolysis at conserved nucleotide-binding domains (NBDs) to diverse cellular functions. Most superfamily members are transporters, while cystic fibrosis transmembrane conductance regulator (CFTR), alone, is an ion channel. Despite this functional difference, recent results have suggested that CFTR shares a common molecular mechanism with other members. ATP binds to partial binding sites on the surface of the two NBDs, which then associate to form a NBD dimer, with complete composite catalytic sites now buried at the interface. ATP hydrolysis and gamma-phosphate dissociation, with the loss of molecular contacts linking the two sides of the composite site, trigger dimer dissociation. The conformational signals generated by NBD dimer formation and dissociation are transmitted to the transmembrane domains where, in transporters, they drive the cycle of conformational changes that translocate the substrate across the membrane; in CFTR, they result in opening and closing (gating) of the ion-permeation pathway.     

Evaluation of the cold-active Pseudoalteromonas haloplanktis β-galactosidase enzyme for lactose hydrolysis in whey permeate as primary step of d-tagatose production

d-Tagatose is an innovative natural low-calorie bulk sweetener with a broad potential for low-calorie and low-glycaemic foods and drinks. Production of this healthy sweetener is realized through enzymatic d-galactose isomerization. d-Galactose needs to be produced in situ due to its limited availability. Whey permeate contains a substantial amount of lactose, which is an interesting source for d-galactose production through enzymatic lactose hydrolysis. In this context, the cold-active β-galactosidase from the psychrophile Pseudoalteromonas haloplanktis was studied. Optimal parameters for efficient lactose hydrolysis in whey permeate have been deduced, viz. optimal incubation temperature, pH and lactose concentration. Hydrolysis efficiencies above 96.0% were realized within 24 h at 23 °C and pH 7.0 in whey permeate with a maximum dry matter content of 10.0% (w/w). In addition, the effect of the presence of d-glucose and d-galactose was investigated up to concentrations of 100 g l⁻¹. d-Glucose inhibited lactose hydrolysis more strongly compared to d-galactose. Also, the operational stability of the cold-active β-galactosidase was studied. Hydrolysis efficiencies above 90.0% were maintained during 7 subsequent hydrolysis cycles.     

A modified pBR322 vector with improved properties for the cloning, recovery, and sequencing of blunt-ended DNA fragments

The construction of a plasmid vector which facilitates the cloning and recovery of blunt-ended DNA fragments is described. This plasmid, called pHP34, differs from pBR322 by a 10-bp insertion which introduces a unique SmaI site immediately flanked by two EcoRI sites. Blunt-ended DNA fragments cloned in the SmaI site can be recovered by digestion with EcoRI. Small cloned fragments can be chemically sequenced using a strategy which does not require their purification. The use of a plasmid related to pHP34 for in vitro mutagenesis by the insertion of a DNA linker fragment conferring an antibiotic resistance is also discussed.