The binding of cholera toxin to the periplasmic vestibule of the type II secretion channel

The type II secretion system (T2SS) is a large macromolecular complex spanning the inner and outer membranes of many Gram-negative bacteria. The T2SS is responsible for the secretion of virulence factors such as cholera toxin (CT) and heat-labile enterotoxin (LT) from Vibrio cholerae and enterotoxigenic Escherichia coli, respectively. CT and LT are closely related AB₅ heterohexamers, composed of one A subunit and a B-pentamer. Both CT and LT are translocated, as folded protein complexes, from the periplasm across the outer membrane through the type II secretion channel, the secretin GspD. We recently published the 19 Å structure of the V. cholerae secretin (VcGspD) in its closed state and showed by SPR measurements that the periplasmic domain of GspD interacts with the B-pentamer complex. Here we extend these studies by characterizing the binding of the cholera toxin B-pentamer to VcGspD using electron microscopy of negatively stained preparations. Our studies indicate that the pentamer is captured within the large periplasmic vestibule of VcGspD. These new results agree well with our previously published studies and are in accord with a piston-driven type II secretion mechanism.Key words: secretin, GspD, electron cryomicroscopy, type II secretion system (T2SS), cholera toxin     

Discrimination of Kalopanax pictus from its varieties and other ‘Kalopanacis Cortex’ plants by multiplex polymerase chain reaction (PCR)

‘Kalopanacis Cortex’ (KC) is an important medicinal material prescribed in Korea for the treatment of various ailments such as paralysis, arthritis, and rheumatism. In Korea, KC is defined as the dried stem bark of Kalopanax pictus. However, the stem barks of Zanthoxylum ailanthoides and Erythrina plants such as E. variegata have also been described as KC and prescribed for the same diseases. Since the pharmacological activities and contents of compounds isolated from the stem barks of these KC plants are obviously different, KC from K. pictus should be clearly discriminated from other stem bark in the best interest of public health. This study sequenced the internal transcribed spacers (ITS) of 52 samples of the KC or KC plants collected from Korea, China, and Vietnam. On the basis of different nucleotide sequences of specific ITS regions among the KC plants, the primer set KP F2/KC R1 was designed to amplify a 398-bp DNA marker for discriminating K. pictus from its varieties and from other KC plants. This primer set, along with the primer sets ZR F1/ZR R4, KP F1/EV R2, and KPF1/KC R1, was successfully amplified with the DNA markers of the Z. ailanthoides, E. variegata, and K. pictus taxa, respectively. The multiplex polymerase chain reaction method developed here not only discriminates the stem bark of K. pictus from stem barks of other KC plants but also identifies KC plants that supply KC in a single process.     

Generation of trophoblast stem cells from rabbit embryonic stem cells with BMP4

Trophoblast stem (TS) cells are ideal models to investigate trophectoderm differentiation and placental development. Herein, we describe the derivation of rabbit trophoblast stem cells from embryonic stem (ES) cells. Rabbit ES cells generated in our laboratory were induced to differentiate in the presence of BMP4 and TS-like cell colonies were isolated and expanded. These cells expressed the molecular markers of mouse TS cells, were able to invade, give rise to derivatives of TS cells, and chimerize placental tissues when injected into blastocysts. The rabbit TS-like cells maintained self-renewal in culture medium with serum but without growth factors or feeder cells, whilst their proliferation and identity were compromised by inhibitors of FGFs and TGF-β receptors. Taken together, our study demonstrated the derivation of rabbit TS cells and suggested the essential roles of FGF and TGF-β signalings in maintenance of rabbit TS cell self-renewal.     

Understanding plant-microbe interactions for phytoremediation of petroleum-polluted soil

Plant-microbe interactions are considered to be important processes determining the efficiency of phytoremediation of petroleum pollution, however relatively little is known about how these interactions are influenced by petroleum pollution. In this experimental study using a microcosm approach, we examined how plant ecophysiological traits, soil nutrients and microbial activities were influenced by petroleum pollution in Phragmites australis, a phytoremediating species. Generally, petroleum pollution reduced plant performance, especially at early stages of plant growth. Petroleum had negative effects on the net accumulation of inorganic nitrogen from its organic forms (net nitrogen mineralization (NNM)) most likely by decreasing the inorganic nitrogen available to the plants in petroleum-polluted soils. However, abundant dissolved organic nitrogen (DON) was found in petroleum-polluted soil. In order to overcome initial deficiency of inorganic nitrogen, plants by dint of high colonization of arbuscular mycorrhizal fungi might absorb some DON for their growth in petroleum-polluted soils. In addition, through using a real-time polymerase chain reaction method, we quantified hydrocarbon-degrading bacterial traits based on their catabolic genes (i.e. alkB (alkane monooxygenase), nah (naphthalene dioxygenase) and tol (xylene monooxygenase) genes). This enumeration of target genes suggests that different hydrocarbon-degrading bacteria experienced different dynamic changes during phytoremediation and a greater abundance of alkB was detected during vegetative growth stages. Because phytoremediation of different components of petroleum is performed by different hydrocarbon-degrading bacteria, plants' ability of phytoremediating different components might therefore vary during the plant life cycle. Phytoremediation might be most effective during the vegetative growth stages as greater abundances of hydrocarbon-degrading bacteria containing alkB and tol genes were observed at these stages. The information provided by this study enhances our understanding of the effects of petroleum pollution on plant-microbe interactions and the roles of these interactions in the phytoremediation of petroleum-polluted soil.     

Seroprevalence of pandemic (H1N1) 2009 in pregnant women in China: an observational study

Background

We investigated the seropositive rates and persistence of antibody against pandemic (H1N1) 2009 virus (pH1N1) in pregnant women and voluntary blood donors after the second wave of the pandemic in Nanjing, China.

Methodology/Principal Findings

Serum samples of unvaccinated pregnant women (n = 720) and voluntary blood donors (n = 320) were collected after the second wave of 2009 pandemic in Nanjing. All samples were tested against pH1N1 strain (A/California/7/2009) with hemagglutination inhibition assay. A significant decline in seropositive rates, from above 50% to about 20%, was observed in pregnant women and voluntary blood donors fifteen weeks after the second wave of the pandemic. A quarter of the samples were tested against a seasonal H1N1 strain (A/Brisbane/59/2007). The antibody titers against pH1N1 strain were found to correlate positively with those against seasonal H1N1 strain. The correlation was modest but statistically significant.

Conclusions and Significance

The high seropositive rates in both pregnant women and voluntary blood donors suggested that the pH1N1 virus had widely spread in these two populations. Immunity derived from natural infection seemed not to be persistent well.     

Research progress of RNA quadruplex

RNA/DNA sequences rich in guanine (G) can form a 4-strand structure, G-quadruplex, which has been extensively researched and observed in mammalian, fungi, and plants, with in vivo existence in eukaryotic cells. Compared with DNA quadruplex, the potential existence of RNA quadruplex appears to be generally rare; however, it is believed by some researchers to be more inevitable in vivo and speculated to play an important role where it exists. Recently, researches concerning the function of G-quadruplexes in RNAs commence, making much progress. However, there is no available review particularly focusing on RNA quadruplex till now as we know. Therefore, we decide to give a review to comprehensively summarize research progress on it. This review highlights the diverse topologies for RNA quadruplex structure and its effect factors; outlines the current knowledge of RNA quadruplex's physiological functions in biological systems, especially in gene expression; and presents the prospects of RNA quadruplex.     

小羽贯众提取物抗菌活性的初步研究

目的:比较小羽贯众根状茎和叶提取物体外抑菌活性。方法:牛津杯法和96孔板法,通过测定抑菌圈大小、最小抑菌浓度(MIC)和最小杀菌浓度(MBC),比较小羽贯众根状茎和叶提取物分别对10种常见细菌的抑制作用,以及不同产地抑菌效果的比较。结果:小羽贯众的根状茎和叶的提取物对10种常见的细菌均表现出较强的抑菌活性,肺炎克雷伯氏菌对提取物最敏感。结论:小羽贯众提取物作为一种天然的抗菌物质,具有广谱抗菌效果,有较高的应用潜力和开发前景。     

颧颞部骨折术后并发颞部凹陷的临床回顾性研究

目的:分析不同颧颞部骨折性质与颞部凹陷的相关性,评价颧颞部骨折术后并发颞部凹陷的防治效果。方法:对105例颧颞部骨折病例进行回顾性分析,52例患者行颞部凹陷修复术,采用头皮冠状切口,应用钛网修复颞部凹陷,术后通过长期随访评价治疗效果。结果:陈旧性骨折颞部凹陷的发生率显著高于新鲜骨折,但治疗后颞部外形均有明显改善。结论:钛网植入能有效地修复颧颞部骨折术后并发的颞部凹陷,但应把握手术时机及治疗方法。     

CBR2激活与小胶质细胞的活化和损伤的关系

目的:探讨大麻素CBR2受体激动剂AM1241预处理对脂多糖(LPS)和γ-干扰素(IFN-γ)所致炎症反应对小胶质细胞活化和损伤的影响。方法:联用LPS和IFN-γ作为小胶质细胞损伤模型,将细胞分为Control组、AM1241组、LPS/IFN-γ组和AM1241+LPS/IFN-γ组;AM1241组和AM1241+LPS/IFN-γ组经AM1241预处理2h,LPS/IFN-γ组和AM1241+LPS/IFN-γ组用含LPS和IFN-γ的培养基培养24h。采用MTT法检测细胞代谢率,硝酸还原酶法检测细胞培养液中一氧化氮(NO)释放量,酶联免疫吸附剂测定细胞培养基中炎症因子释放量,倒置相差显微镜观察细胞形态。结果:与LPS/IFN-γ组相比,AM1241+LPS/IFN-γ组细胞代谢率明显升高(P<0.05),NO、TNF-α、IL-1β和IL-10释放量明显减少(P<0.05),活化和损伤程度明显减轻。结论:大麻素CBR2受体激动剂AM1241预处理可减轻LPS和IFN-γ对小胶质细胞的活化和损伤。