Strategies to Improve/Eliminate the Limitations in Shotgun Lipidomics

Direct infusion‐based shotgun lipidomics is one of the most powerful and useful tools in comprehensive analysis of lipid species from lipid extracts of various biological samples with high accuracy/precision. However, despite many advantages, the classical shotgun lipidomics suffers some general dogmas of limitations, such as ion suppression, ambiguous identification of isobaric/isomeric lipid species, and ion source–generated artifacts, restraining the applications in analysis of low‐abundance lipid species, particularly those less ionizable or isomers that yield almost identical fragmentation patterns. This article reviews the strategies (such as modifier addition, prefractionation, chemical derivatization, charge feature utilization) that have been employed to improve/eliminate these limitations in modern shotgun lipidomics approaches (e.g., high mass resolution mass spectrometry–based and multidimensional mass spectrometry–based shotgun lipidomics). Therefore, with the enhancement of these strategies for shotgun lipidomics, comprehensive analysis of lipid species including isomeric/isobaric species is achieved in a more accurate and effective manner, greatly substantiating the aberrant lipid metabolism, signaling trafficking, and homeostasis under pathological conditions.     

Naphthyridine tetramer with a pre-organized structure for 1:1 binding to a CGG/CGG sequence

A naphthyridine carbamate dimer (NCD) is a synthetic ligand for DNA containing a CGG/CGG sequence. Although NCD can bind selectively and tightly to a CGG/CGG sequence, the highly cooperative 2:1 binding mode has hampered precise analysis of the binding. We describe herein the synthesis of a series of naphthyridine tetramers consisting of two NCD molecules connected with various linkers to seek a ligand that binds to a CGG/CGG sequence exclusively with a 1:1 stoichiometry. Among the tested ligands, NCTB and Z-NCTS, which have linker moieties with restricted conformational flexibility [biphenyl and (Z)-stilbene linker, respectively], gave the exclusive formation of a 1:1 ligand-CGG/CGG complex. The (Z)-stilbene linker in Z-NCTS was designed to have pre-organized conformation appropriate for the binding and, in fact, resulted in the highest binding affinity. Thermodynamic parameters obtained by isothermal titration calorimetry indicated that the stronger binding of Z-NCTS was attributed to its lower entropic cost. The present study provides not only a novel 1:1 binding ligand, but also valuable feedback for subsequent molecular design of DNA and RNA binding ligands.     

Genome Sequence of Pseudomonas aeruginosa Strain AH16, Isolated from a Patient with Chronic Pneumonia in China

Pseudomonas aeruginosa AH16 is a virulent strain isolated from a patient with chronic pneumonia in China. Here, we present a 6.8-Mb (G+C content, 66.13%) assembly of its genome with 6,332 putative coding sequences, which may provide insights into the genomic basis of activity of the clinical P. aeruginosa strain in China.     

羽衣甘蓝对镉的耐性和富集特征研究

以观赏绿化植物羽衣甘蓝(Brassica oleracea L.var.acephala DC.)为试验材料,采用盆栽试验,研究其对镉的耐性和富集特征,探讨羽衣甘蓝对镉污染土壤生物修复的可行性。结果显示:(1)随着镉处理浓度的增加,羽衣甘蓝干重呈先升高后降低的趋势,20~80mg·kg-1镉处理能促进植株的生长,100~120mg·kg-1镉处理虽然显著抑制了根系的生长,但是促进了地上部的生长,整体而言对全株生长无明显影响,表明羽衣甘蓝对镉有较强的耐性,且地上部的耐性高于根系。(2)所有镉处理下,羽衣甘蓝叶片的SOD、POD和APX活性较高,MDA含量和电解质渗漏率与对照无差异;而镉处理浓度高于80mg·kg-1时,根系的SOD、CAT和APX活性显著降低,MDA含量和电解质渗漏率显著升高,引起严重的膜脂过氧化伤害,这可能是羽衣甘蓝地上部的镉耐性高于根系的原因之一。(3)羽衣甘蓝地上部的镉含量高于根系,且随着镉处理浓度的增加均逐渐增加,在镉处理浓度为120mg·kg-1时达到最大值,分别为50.15mg·kg-1(根系)和52.01mg·kg-1(地上部);植株对镉的转运系数大于1,地上部镉富集量高于根系,地上部最大富集量为每株343.19μg。研究表明,羽衣甘蓝对镉有很强的耐性和富集、转运能力,是一种良好的修复镉污染土壤的观赏绿化植物资源。     

以米蛾卵为寄主繁殖玉米螟赤眼蜂的质量控制技术

以米蛾卵为寄主繁殖玉米螟赤眼蜂的质量控制技术包括:米蛾卵的清理和优选,优质种蜂的准备,接蜂过程的条件调控,生产用蜂的收集、清理和质量检测.     

Influence of frequency and temperature on the mechanisms of nerve conduction block induced by high-frequency biphasic electrical current

The influences of stimulation frequency and temperature on mechanisms of nerve conduction block induced by high-frequency biphasic electrical current were investigated using a lumped circuit model of the myelinated axon based on Schwarz and Eikhof (SE) equations. The simulation analysis showed that a temperature-frequency relationship was determined by the axonal membrane dynamics (i.e. how fast the ion channels can open or close.). At a certain temperature, the axonal conduction block always occurred when the period of biphasic stimulation was smaller than the action potential duration (APD). When the temperature decreased from 37 to 15 degrees C, the membrane dynamics slowed down resulting in an APD increase from 0.4 to 2.4 ms accompanied by a decrease in the minimal blocking frequency from 4 to 0.5 kHz. The simulation results also indicated that as the stimulation frequency increased the mechanism of conduction block changed from a cathodal/anodal block to a block dependent upon continuous activation of potassium channels. Understanding the interaction between the minimal blocking frequency and temperature could promote a better understanding of the mechanisms of high frequency induced axonal conduction block and the clinical application of this method for blocking nerve conduction.     

Ligand-inducible formation of RNA pseudoknot

Here, we demonstrate that a series of naphthyridine derivatives, naphthyridine carbamate tetramer (NCTn), can bind to the RNA CGG/CGG triad comprised of two single-stranded regions of a hairpin loop and a tail. Complete suppression of the binding by a single mutation indicated simultaneous binding of NCTn between hairpin loop and single stranded tail, leading to the formation of NCTn-induced pseudoknot.     

Analysis of nerve conduction block induced by direct current

The mechanisms of nerve conduction block induced by direct current (DC) were investigated using a lumped circuit model of the myelinated axon based on Frankenhaeuser–Huxley (FH) model. Four types of nerve conduction block were observed including anodal DC block, cathodal DC block, virtual anodal DC block, and virtual cathodal DC block. The concept of activating function was used to explain the blocking locations and relation between these different types of nerve block. Anodal/cathodal DC blocks occurred at the axonal nodes under the block electrode, while virtual anodal/cathodal DC blocks occurred at the nodes several millimeters away from the block electrode. Anodal or virtual anodal DC block was caused by hyperpolarization of the axon membrane resulting in the failure of activating sodium channels by the arriving action potential. Cathodal or virtual cathodal DC block was caused by depolarization of the axon membrane resulting in inactivation of the sodium channel. The threshold of cathodal DC block was lower than anodal DC block in most conditions. The threshold of virtual anodal/cathodal blocks was about three to five times higher than the threshold of anodal/cathodal blocks. The blocking threshold was decreased with an increase of axonal diameter, a decrease of electrode distance to axon, or an increase of temperature. This simulation study, which revealed four possible mechanisms of nerve conduction block in myelinated axons induced by DC current, can guide future animal experiments as well as optimize the design of electrodes to block nerve conduction in neuroprosthetic applications.