Lipopolysaccharides and polysaccharides of the cell envelope of toxic Microcystis aeruginosa strains

The effect of the removal of signal peptides after cleavage of precursor molecules by the signal peptidase I was examined in an in vitro translocation system with Escherichia coli membrane vesicles. The translocation of periplasmic alkaline phosphatase precursors was significantly inhibited by the protease inhibitors antipain, elastatinal and leupeptin. Antipain and leupeptin enhanced the translocation of precursors of outer membrane protein OmpA, but inhibited the processing. However, antipain did not inhibit the processing of precursors mediated by signal peptidase I in the soluble form. Moreover, the inhibition by antipain was not due to the disruption of membrane integrity, but occurred during the process of protein translocation. Since these small peptide inhibitors are known to inhibit membrane protease IV, a signal peptide peptidase, these results suggest that the hydrolysis of signal peptides is an important step in the recycles of the overall translocation process, and that the prevention of degradation of signal peptides feedback inhibits the preceding steps in the translocation pathway.Dedicated to John L. Ingraham on the occasion of his retirement; his approaches and enthusiasm for science remain an inspiration to PCT, who has been guided by his motto, Science should be fun, for the last twenty years     

Lack of specific hybridization between the lep genes of Salmonella typhimurium and Bacillus licheniformis

The rfb gene cluster which determines the biosynthesis of the O2 O antigen has been cloned from an Escherichia coli O2: K1 strain isolated from a case of septicaemia in chickens. The region required for expression of the O antigen in E. coli K-12 was localised to a 10.7 to 14.15-kb segment which was shown to be chromosomal in origin with a close linkage to the gnd and his genetic loci.     

Cellular expression and alternative splicing of SLC25A23, a member of the mitochondrial Ca2+-dependent solute carrier gene family

Phospholipase D (PLD) is a ubiquitous enzyme in eukaryotes that participates in various cellular processes. Its catalytic domain is characterized by two HKD motifs in the C-terminal part. Until now, two subfamilies were recognized based on their N-terminal domain structure. The first has a PX domain in combination with a PH domain and is designated as PXPH-PLD. Members of the second subfamily, named C2-PLD, have a C2 domain and have, so far, only been found in plants. Here we describe a novel PLD subfamily that we identified in Phytophthora, a genus belonging to the class oomycetes and comprising many important plant pathogens. We cloned Pipld1 from Phytophthora infestans and retrieved full-length sequences of its homologues from Phytophthora sojae and Phytophthora ramorum genome databases. Their promoters contain two putative regulatory elements, one of which is highly conserved in all three genes. The three Phytophthora pld1 genes encode nearly identical proteins of around 1807 amino acids, with the two characteristic HKD motifs in the C-terminal part. Homology of the predicted proteins with known PLDs however is restricted to the two catalytic HKD motifs and adjacent domains. In the N-terminal part Phytophthora PLD1 has a PX-like domain, but it lacks a PH domain. Instead the N-terminal region contains five putative membrane spanning domains suggesting that Phytophthora PLD1 is a transmembrane protein. Since Phytophthora PLD1 cannot be categorized in one of the two existing subfamilies we propose to create a novel subfamily named PXTM-PLD.     

Autocrine activation of ion currents in the two-cell mouse embryo

The actions of autocrine ligands are required for the normal development of the preimplantation embryo in vitro. These ligands act as survival factors for the preimplantation stage embryo. One autocrine ligand, paf (1-o-alkyl-2-acetyl-sn-gylcero-3-phosphocholine), induced a dihydropyridine-sensitive calcium transient in the zygote and two-cell embryo, and these transients were required for the normal preimplantation stage survival. Paf induces an influx of external calcium through a dihydropyridine-sensitive channel. Dihydropyridine-sensitive currents are voltage-regulated, yet to date there is no evidence of membrane voltage depolarization in the two-cell embryo. To define the paf-induced calcium influx we have examined the response of the membrane potential and ion currents to paf in two-cell embryos. An initial response to paf challenge was the expression of an ion current (-15.6+/-1.6 pA) that was dependent upon extracellular calcium, was not voltage-gated but was dihydropyridine (nifedipine)-sensitive. This calcium current was followed (91+/-6 s after paf) by a net outward current (284+/-59 pA) that was composed of 4,4'-diisothiocyanatostilbene-2,2'-disulfonate-sensitive (anion channel blocker) and tetraethylammonium chloride-sensitive (K(+) channel blocker) currents. This current corresponded temporally with a marked paf-induced transient hyperpolarization of the membrane potential (-8.4+/-1.2 mV) that was dependent upon the generation of the calcium transient. The results directly demonstrate the activation of a voltage-independent calcium current in response to paf and show for the first time the expression of an afterhyperpolarization that occurs as a response to the calcium transient.     

植物赤霉素矮化突变体研究进展

赤霉素(GAs)在植物种子萌发、茎的伸长和花的发育等方面起着非常重要的作用。近年来,随着研究手段和技术不断进步,对赤霉素(GA)生物合成和信号传导过程中相关基因的研究取得了惊人的进展。与GA有关的矮化突变体主要有GA缺陷型和不敏感型两类,本文对与GA生物合成和信号传导过程中有关的这两类矮突变体的研究进展进行综述。对这些这些突变体的研究促进了对赤霉素生物合成和信号传导途径的认识,同时为赤霉素更好地利用提供了科学依据。     

Brefeldin A induces callose formation in onion inner epidermal cells

Summary The antibiotic fungal toxin brefeldin A (BFA) causes synthesis of additional cell wall material in adult differentiated onion inner epidermal cells at concentrations of 5–30 g/ml. This tertiary wall contains callose and is layered on the secondary cellulosic wall in a time- and dose-dependent manner. Initially, callose is found in pit fields in the form of small vesicular patches. With time and dose, depositions grow in size and form large plugs invaginating into the cell, where the adjacent cytoplasm forms bulky accumulations and contains many organelles including endomembranes. Within the cytoplasm, BFA exerts the characteristic morphological effects on the secretory system including changes of the Golgi stacks, formation of large vesicles, and proliferation of dilated cisternae of the endoplasmic reticulum. Higher concentrations of BFA (60 g/ml) lead to disintegration of the Golgi apparatus; they have no effects on the cell wall, no callose synthesis occurs. We conclude from these observations that BFA has two independent targets in onion cells. BFA acts on the plasma membrane, hence operating as an elicitor of plant defense reactions and thus activates callose synthesis. BFA acts also on the membranes of the secretory system and influences budding and fusion of vesicles at the endoplasmic reticulum and at the dictyosomes. These two mechanisms occur in parallel, suggesting that the secretory system still can play its presumed role in callose synthesis. Only when dictyosomes are completely disintegrated, no more callose is formed.Abbreviations BFA Brefeldin A - PM plasma membrane - GA Golgi apparatus - ER endoplasmic reticulum - GS glucan synthetase Dedicated to Professor Walter Gustav Url on the occasion of his 70th birthday     

Myocardial Hsp70 phosphorylation and PKC-mediated cardioprotection following exercise

Both protein kinase C (PKC) activation and Hsp70 expression have been shown to be key components for exercise-mediated myocardial protection during ischemia-reperfusion injury. Given that Hsp70 has been shown to undergo inducible phosphorylation in striated muscle and liver, we hypothesized that PKC may regulate myocardial Hsp70 function and subsequent exercise-conferred cardioprotection through this phosphorylation. Hence, acute exercise of male Sprague-Dawley rats (30 m/min for 60 min at 2% grade) was employed to assess the role of PKC and its selected isoforms in phosphorylation of Hsp70 and protection of the myocardium during ischemia-reperfusion injury. It was observed that administration of the PKC inhibitor chelerythrine chloride (5 mg/kg) suppressed the activation of three exercise-induced PKC isoforms (PKCalpha, PKCdelta, and PKCepsilon) and attenuated the exercise-mediated reduction of myocardial infarct size during ischemia-reperfusion injury. While this study also demonstrated that exercise led to an alteration in the phosphorylation status of Hsp70, this posttranslational modification appeared to be dissociated from PKC activation, as exercise-induced phosphorylation of Hsp70 was unchanged following inhibition of PKC. Taken together, these results indicate that selected isoforms of PKC play an important role in exercise-mediated protection of the myocardium during ischemia-reperfusion injury. However, exercise-induced phosphorylation of Hsp70 does not appear to be a mechanism by which PKC induces this cardioprotective effect.     

一种改进的小波阈值法去除耳声发射中的伪迹

本文探讨了耳声发射及其分类、特性、目前存在的问题和相关研究方法,并提出一种改进的小波阈值处理方法,它是基于一种多分辨分析小波阈值去噪,在传统的软、硬阈值去噪基础上设立两个变量,通过调节这两个变量有效地达到去除噪声的效果。     

HAMP domain signal relay mechanism in a sensory rhodopsin-transducer complex

The phototaxis receptor complex composed of sensory rhodopsin II (SRII) and the transducer subunit HtrII mediates photorepellent responses in haloarchaea. Light-activated SRII transmits a signal through two HAMP switch domains (HAMP1 and HAMP2) in HtrII that bridge the photoreceptive membrane domain of the complex and the cytoplasmic output kinase-modulating domain. HAMP domains, widespread signal relay modules in prokaryotic sensors, consist of four-helix bundles composed of two helices, AS1 and AS2, from each of two dimerized transducer subunits. To examine their molecular motion during signal transmission, we incorporated SRII-HtrII dimeric complexes in nanodiscs to allow unrestricted probe access to the cytoplasmic side HAMP domains. Spin-spin dipolar coupling measurements confirmed that in the nanodiscs, SRII photoactivation induces helix movement in the HtrII membrane domain diagnostic of transducer activation. Labeling kinetics of a fluorescein probe in monocysteine-substituted HAMP1 mutants revealed a light-induced shift of AS2 against AS1 by one-half α-helix turn with minimal other changes. An opposite shift of AS2 against AS1 in HAMP2 at the corresponding positions supports the proposal from x-ray crystal structures by Airola et al. (Airola, M. V., Watts, K. J., Bilwes, A. M., and Crane, B. R. (2010) Structure 18, 436-448) that poly-HAMP chains undergo alternating opposite interconversions to relay the signal. Moreover, we found that haloarchaeal cells expressing a HAMP2-deleted SRII-HtrII exhibit attractant phototaxis, opposite from the repellent phototaxis mediated by the wild-type di-HAMP SRII-HtrII complex. The opposite conformational changes and corresponding opposite output signals of HAMP1 and HAMP2 imply a signal transmission mechanism entailing small shifts in helical register between AS1 and AS2 alternately in opposite directions in adjacent HAMPs.     

A conserved non-canonical motif in the pseudoactive site of the ROP5 pseudokinase domain mediates its effect on Toxoplasma virulence

The ROP5 family is a closely related set of polymorphic pseudokinases that are critical to the ability of Toxoplasma to cause disease. Polymorphisms in ROP5 also make it a major determinant of strain-specific differences in virulence. ROP5 possesses all of the major kinase motifs required for catalysis except for a substitution at the catalytic Asp. We show that this substitution in the catalytic loop of ROP5 is part of a motif conserved in other pseudokinases of both Toxoplasma and human origin, and that this motif is required for the full activity in vivo of ROP5. This suggests evolutionary selection at this site for a biochemical function, rather than simple drift away from catalysis. We present the crystal structures of a virulent isoform of ROP5 both in its ATP-bound and -unbound states and have demonstrated that despite maintaining the canonical ATP-binding motifs, ROP5 binds ATP in a distorted conformation mediated by unusual magnesium coordination sites that would not be predicted from the primary sequence. In addition, we have mapped the polymorphisms spread throughout the primary sequence of ROP5 to two major surfaces, including the activation segment of ROP5. This suggests that the pseudoactive site of this class of pseudokinases may have evolved to use the canonical ATP-binding motifs for non-catalytic signaling through allostery.     

Phosphorylation of Thr-516 and Ser-520 in the Kinase Activation Loop of MEKK3 Is Required for Lysophosphatidic Acid-mediated Optimal I��B Kinase �� (IKK��)/Nuclear Factor-��B (NF-��B) Activation

MEKK3 serves as a critical intermediate signaling molecule in lysophosphatidic acid-mediated nuclear factor-κB (NF-κB) activation. However, the precise regulation for MEKK3 activation at the molecular level is still not fully understood. Here we report the identification of two regulatory phosphorylation sites at Thr-516 and Ser-520 within the kinase activation loop that is essential for MEKK3-mediated IκB kinase β (IKKβ)/NF-κB activation. Substitution of these two residues with alanine abolished the ability of MEKK3 to activate IKKβ/NF-κB, whereas replacement with acidic residues rendered MEKK3 constitutively active. Furthermore, substitution of these two residues with alanine abolished the ability of MEKK3 to mediate lysophosphatidic acid-induced optimal IKKβ/NF-κB activation.     

The Paradoxical Anthropology of Leslie White

The many contradictions in the anthropology of Leslie White derive mainly from the fact that he embraced two contradictory models of culture: the sui generis conception that he received from his Boasian education, and the materialist-utilitarian framework that developed out of his concern with cultural evolutionism. White never reconciled the two, but in any instance of conflict he gave preference to the sui generis, Boasian-derived conception. This led him eventually to repudiate significant aspects of his utilitarian-adaptive framework.     

应力作用下软骨细胞信号传导的研究进展

研究显示应力刺激对软骨细胞生长及基质代谢具重要作用。软骨正常结构形态以及应力下的软骨细胞形态和基质代谢的变化是力-生物信号转化的基础,信号分子及信号通路则是应力信号传导的核心,二者是对软骨细胞应力下信号传导过程深入了解不可或缺的信息组成,了解应力对软骨细胞的作用方式及作用机制有助于软骨相关疾病诊治、组织工程等领域的研究,本文就这两个方面研究进展做一综述。     

Ethylene Receptors: Ethylene Perception and Signal Transduction

Ethylene is sensed by a family of receptors that can be divided into two subfamilies based on phylogenetic analysis and some shared structural features. In this review we focus on the mechanistic aspects of how the receptors function in plants to transduce the ethylene signal. Recent work has led to new insights into how ethylene binds to the receptors and how this binding may induce a conformational change to regulate signaling. Additional studies point to several possible mechanisms for signal output by the receptors, which may involve changes in enzymatic activity and/or conformational changes. Other studies indicate the importance of interactions, both physical and genetic, between the receptors and early components of the signaling pathway, in particular, the Raf-like kinase CTR1, which functions as an integral component of the ethylene receptor signaling complex. The current model for signaling in Arabidopsis supports differing contributions from the receptors, with subfamily-1 receptors playing a more significant role than the subfamily-2 receptors in transmitting the ethylene signal.     

Frequency modulation patterns in the echolocation signals of two vespertilionid bats

In this study we measure and classify frequency modulation patterns in echolocation signals of two species of bats. By using the derivative of an exponential model fitted to pulses emitted by Pipistrellus pipistrellus and Myotis myotis, we show that the modulation functions differ fundamentally between the two species and also vary within each species. This variation makes it unlikely that pulse design and the concomitant modulation pattern can be explained by a single common principle as previously suggested.     

Marginality,ethnicity and penality: a response to Loïc Wacquant

This article responds to Loïc Wacquant's elaboration of his overarching theoretical framework in his stimulating article ‘Marginality, Ethnicity and Penality in the Neo-liberal City: An Analytic Cartography’. I raise some issues that he might reflect on in his rejoinder to the comments on his essay. These include: (1) the need for greater specification and clarification of explanatory and conceptual variables in the elaboration of his theoretical framework, especially theoretical mechanisms and two key concepts, ‘precariat’ and ‘neo-liberal policy’; and (2) addressing a major study offering empirically based arguments that indirectly challenge assertions in his theoretical framework.     

Heterologous expression,secretion and characterization of the <Emphasis Type="Italic">Geobacillus thermoleovorans</Emphasis> US105 type I pullulanase

Pullulanase type I of Geobacillus thermoleovorans US105 strain (PUL US105) was produced and secreted efficiently in the E. coli periplasmic or extracellular fraction using two different signal peptides. Hence, the open reading frame was connected downstream of the lipase A signal peptide of Bacillus subtilis strain leading to an efficient secretion of an active form enzyme on the periplasmic fraction. In addition, pul US105 was fused to the α-amylase signal sequence of the Bacillus stearothermophilus US100 strain. The monitoring of the pullulanase activity and Western blot analysis for this last construction showed that the most activity was found in the supernatant culture, proving the efficient secretion of this natively cytoplasmic enzyme as an active form. The PUL US105 was purified to homogeneity from the periplasmic fraction, using heat treatment, size exclusion, and anion-exchange chromatography. The native pullulanase has a molecular mass of 160 kDa and is composed of two identical subunits of 80 kDa each. It was independent for metallic ions for its activity, while its thermostability was obviously improved in presence of only 0.1 mM CaCl₂.     

邹承鲁先生两项被收入教科书的研究成果

邹承鲁先生出生于1923年5月17日，1951年于英国剑桥大学获博士学位。他长期从事蛋白质结构与功能的研究，作为近代中国生物化学的奠基人之一，在酶学研究领域做出了具有重要意义的工作。为了纪念邹承鲁先生诞辰100周年，特将邹先生60年前完成的两项重要的研究成果（蛋白质必需基团修饰程度和活性丧失的定量关系，酶活性不可逆抑制动力学）较详细地介绍给读者。希望通过本文的介绍，使读者看到老一辈科学家“是如何在资源匮乏的条件下，运用自己的聪明才智取得成就”的范例。     

人骨髓瘤细胞中两条IL-6信号转导途径的相互调控方式

首先利用凝胶阻滞电泳 ( electrophoretic mobility shift assay,EMSA )和免疫沉淀( immunoprecipitation,IP)方法观察两条 IL- 6信号转导途径—— JAK/STAT和 Ras/NF- IL- 6在人骨髓瘤细胞系 Sko- 0 0 7中的诱导激活状态 ;继而采用分别作用于两条途径的蛋白激酶抑制剂或激动剂以及转录因子的反义核酸与 IL- 6共同作用 Sko- 0 0 7细胞 ,观察一条途径激活信号上调 (或下调 )时 ,另外一条途径活化状态的变化 .结果显示 :1 .JAK/STAT和 Ras/NF- IL- 6信号转导途径都能够在 Sko- 0 0 7细胞中诱导激活 ;2 .与 JAK/STAT途径活化相关的某个酪氨酸磷酸化作用参与了Ras途径的诱导激活 ;Ras途径可通过蛋白激酶 MAPK( motigen- activated protein kinase)对 JAK/STAT途径的激活起正调控作用 .这说明在人骨髓瘤细胞 Sko- 0 0 7中两条 IL- 6信号途径可相互调控彼此的活化 .     

植物细胞程序性死亡研究进展

植物细胞死亡分为坏死和程序性死亡。细胞程序性死亡是具有信号或一系列分子参与,并且由细胞内在的死亡程序介导的有序过程。它在植物生长发育和抵御外界胁迫中具有重要作用。简要介绍了植物PCD的特征,对植物PCD中的信号分子和类caspase的作用等进行了综述,并对植物PCD存在的问题进行分析和展望,为深入研究植物PCD提供参考。