PGRP-LB: An Inside View into the Mechanism of the Amidase Reaction

Peptidoglycan recognition proteins (PGRPs) are ubiquitous among animals and play pivotal functions in insect immunity. Non-catalytic PGRPs are involved in the activation of immune pathways by binding to the peptidoglycan (PGN), whereas amidase PGRPs are capable of cleaving the PGN into non-immunogenic compounds. Drosophila PGRP-LB belongs to the amidase PGRPs and downregulates the immune deficiency (IMD) pathway by cleaving meso-2,6-diaminopimelic (meso-DAP or DAP)-type PGN. While the recognition process is well analyzed for the non-catalytic PGRPs, little is known about the enzymatic mechanism for the amidase PGRPs, despite their essential function in immune homeostasis. Here, we analyzed the specific activity of different isoforms of Drosophila PGRP-LB towards various PGN substrates to understand their specificity and role in Drosophila immunity. We show that these isoforms have similar activity towards the different compounds. To analyze the mechanism of the amidase activity, we performed site directed mutagenesis and solved the X-ray structures of wild-type Drosophila PGRP-LB and its mutants, with one of these structures presenting a protein complexed with the tracheal cytotoxin (TCT), a muropeptide derived from the PGN. Only the Y78F mutation abolished the PGN cleavage while other mutations reduced the activity solely. Together, our findings suggest the dynamic role of the residue Y78 in the amidase mechanism by nucleophilic attack through a water molecule to the carbonyl group of the amide function destabilized by Zn²⁺.     

Characterization of the Functional Cross-Talk between Surface GABAA and Dopamine D5 Receptors

The γ-aminobutyric acid type A receptor (GABA_AR) plays a major role in fast inhibitory synaptic transmission and is highly regulated by the neuromodulator dopamine. In this aspect, most of the attention has been focused on the classical intracellular signaling cascades following dopamine G-protein-coupled receptor activation. Interestingly, the GABA_AR and dopamine D5 receptor (D5R) have been shown to physically interact in the hippocampus, but whether a functional cross-talk occurs is still debated. In the present study, we use a combination of imaging and single nanoparticle tracking in live hippocampal neurons to provide evidence that GABA_ARs and D5Rs form dynamic surface clusters. Disrupting the GABA_AR–D5R interaction with a competing peptide leads to an increase in the diffusion coefficient and the explored area of both receptors, and a drop in immobile synaptic GABA_ARs. By means of patch-clamp recordings, we show that this fast lateral redistribution of surface GABA_ARs correlates with a robust depression in the evoked GABAergic currents. Strikingly, it also shifts in time the expression of long-term potentiation at glutamatergic synapses. Together, our data both set the plasma membrane as the primary stage of a functional interplay between GABA_AR and D5R, and uncover a non-canonical role in regulating synaptic transmission.     

预形变和时效Al-2.73Li合金的断裂机制SCIEI

本文研究了预先冷形变对Al-2.73Li合金的机械性能和断裂行为的影响。试验结果表明,预先冷形变使合金的加工硬化率和强度提高,相应损失部分塑性。预先冷形变造成不均匀分布的胞状位错结构及晶界无沉淀带加工硬化,乃是导致塑性下降的主要原因。合金的断裂方式为沿晶和穿晶混合型。预形变后时效使沿晶断裂倾向增大。最后探讨了其断裂机制。     

ELECTRON MICROANALYSIS FOR LASER MELTED ZONE IN 45 STEEL WITH Fe-Ni-Cr COATING

The Fe-Ni-Cr coating laver has been alloyed with 45 steel base metal by transverse.flow typeCO_2 gas laser of maximum output 5kW.The characteristics of the melted zone and the es-sence of the“bright band”has been investigated using the electron microscopy.The resultsshow that the“bright band”belongs to the melted zone and is a vertical section of the planecrystal,The width of the“bright band”equals the height of the plane crystal,which decreaseswith the increase of laser beam scanning rate and the decrease of laser power.This has beenexplained in terms of constitutional supercooling G/R.     

FRACTURE ANALYSIS OF HYDROGEN-INDUCED CRACKING FOR STEEL 12Ni3CrMoV

本文通过插销断口分析,研究了含硼12Ni3CrMoV钢焊接热影响区氢浓度及应力大小与断口形态之间的关系,结果表明,插销断口具有氢脆准解理特征,断口上氢脆准解理区域随氢浓度的升高而增加,随负载应力的加大而减小.准解理断裂面为{110}面.     

La在KCl-NaCl和LaCl_3-KCl-NaCl熔体中的溶解行为SCIEI

本文利用透明槽技术、电化学循环V-A法及量子化学EHMO三种方法,研究了La在KCl-NaCl(1:1mol)及LaCl_3-KCl-NaCl熔体中的溶解行为。初步认为:溶解在KCl-NaCl熔体中的La是以中性金属状态存在。在LaCl_3-KCl-NaCl熔体中,溶解的La与La^(3+)作用生成低价La^(2+)离子,La^(2+)又与周围的La^(3+)作用形成原子簇离子La_m^(n+)赋存于熔体之中。     

SOLUBILITY AND DIFFUSIVITY OF GASES IN AN ORGANIC SOLUTION OF AMINE

Solubilities and diffusivities of carbon dioxide and nitrous oxide in a mixture of toluene and isopropanol organic solution of cyclohexylamine were measured at 20°C in the range of pressures of solute from 1 to 3 bars. This was performed with an original chromatographic technique taking into account the presence of the product of the reaction.     

超滤在明胶生产中的应用

本文研究了超滤在明胶生产中的应用,超滤作为初级浓缩是可行的。同时,对超滤设备、超滤膜与工艺条件作了讨论。     

EXPERIMENTAL INFRARED DRYING STUDY OF A MODEL WATER-BASED EPOXY-AMINE PAINTING COATED ON IRON SUPPORT

The aim of this work is to study the infrared drying and curing kinetics of a model water-based epoxy-amine painting coaled on iron support. After a presentation of the model painting elaborated in our laboratory, experimental and theoretical data of the curing kinetics are presented. Then, we described the special laboratory-scale infrared dryer set up in our laboratory. This dryer was able to carry on drying experiments with uniform infrared flux densities between 0 to 25 kW,m^-2 The study of the painting drying as a function of the infrared flux density and of the film thickness shows the influence of these two main physical parameters.     

Surface chemistry and mechanical property changes of wood‐flour/high‐density‐polyethylene composites after accelerated weathering

Although wood–plastic composites have become more accepted and used in recent years and are promoted as low‐maintenance, high‐durability building products, they do experience a color change and a loss in mechanical properties with accelerated weathering. In this study, we attempted to characterize the modulus‐of‐elasticity (MOE) loss of photostabilized high‐density polyethylene (HDPE) and composites of wood flour and high‐density polyethylene (WF/HDPE) with accelerated weathering. We then examined how weathering changed the surface chemistry of the composites and looked at whether or not the surface changes were related to the MOE loss. By examining surface chemistry changes, we hoped to begin to understand what caused the weathering changes. The materials were left unstabilized or were stabilized with either an ultraviolet absorber or pigment. After 1000 and 2000 h of accelerated weathering, the samples were tested for MOE loss. Fourier transform infrared (FTIR) spectroscopy was employed to monitor carbonyl and vinyl group formation at the surface. Changes in the HDPE crystallinity were also determined with FTIR techniques. It was determined that structural changes in the samples (carbonyl group formation, terminal vinyl group formation, and crystallinity changes) could not be reliably used to predict changes in MOE with a simple linear relationship. This indicated that the effects of crosslinking, chain scission, and crystallinity changes due to ultraviolet exposure and interfacial degradation due to moisture exposure were interrelated factors for the weathering of HDPE and WF/HDPE composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2263–2273, 2004