Diversity of G proteins in signal transduction

The heterotrimeric guanine nucleotide-binding proteins (G proteins) act as switches that regulate information processing circuits connecting cell surface receptors to a variety of effectors. The G proteins are present in all eukaryotic cells, and they control metabolic, humoral, neural, and developmental functions. More than a hundred different kinds of receptors and many different effectors have been described. The G proteins that coordinate receptor-effector activity are derived from a large gene family. At present, the family is known to contain at least sixteen different genes that encode the alpha subunit of the heterotrimer, four that encode beta subunits, and multiple genes encoding gamma subunits. Specific transient interactions between these components generate the pathways that modulate cellular responses to complex chemical signals.     

植株间伤害信息的传递:信号分子及感受机制

植物在遭受到机械损伤或昆虫取食后释放出的伤诱导挥发物,除了具有防御功能外,还可作为伤害信息在植株间传递,引起群体诱导抗性的产生.文中就伤诱导挥发物在植株间传递伤害信息的存在证据、伤害信息分子的可能标准以及植物对伤害信息的感知进行了综述.     

Molecular switch for signal transduction: structural differences between active and inactive forms of protooncogenic ras proteins

Ras proteins participate as a molecular switch in the early steps of the signal transduction pathway that is associated with cell growth and differentiation. When the protein is in its GTP complexed form it is active in signal transduction, whereas it is inactive in its GDP complexed form. A comparison of eight three-dimensional structures of ras proteins in four different crystal lattices, five with a nonhydrolyzable GTP analog and three with GDP, reveals that the "on" and "off" states of the switch are distinguished by conformational differences that span a length of more than 40 A, and are induced by the gamma-phosphate. The most significant differences are localized in two regions: residues 30 to 38 (the switch I region) in the second loop and residues 60 to 76 (the switch II region) consisting of the fourth loop and the short alpha-helix that follows the loop. Both regions are highly exposed and form a continuous strip on the molecular surface most likely to be the recognition sites for the effector and receptor molecule(or molecules). The conformational differences also provide a structural basis for understanding the biological and biochemical changes of the proteins due to oncogenic mutations, autophosphorylation, and GTP hydrolysis, and for understanding the interactions with other proteins.     

Allosteric mechanisms of signal transduction

Forty years ago, a simple model of allosteric mechanisms (indirect interactions between distinct sites), used initially to explain feedback-inhibited enzymes, was presented by Monod, Wyman, and Changeux. We review the MWC theory and its applications for the understanding of signal transduction in biology, and also identify remaining issues that deserve theoretical and experimental substantiation.     

Turnover of inositol phospholipids and signal transduction

Various extracellular informational signals such as those from a group of hormones and some neurotransmitters appear to be passed from the cell surface into the cell interior by two routes, protein kinase C activation and Ca2+ mobilization. Both routes usually become available as the result of an interaction of a single ligand and a receptor and act synergistically to evoke subsequent cellular responses such as release reactions. The signal-dependent breakdown of inositol phospholipids, particularly phosphatidylinositol bisphosphate, now appears to be a key event for initiating these processes.     

盐胁迫下植物的分子信号传导

盐胁迫下,植物体内的离子浓度和渗透压发生变化,诱导其产生第二信使(如IP3和活性氧分子等).第二信使调控细胞内Ca2 的水平,引发蛋白磷酸化级联反应,直接诱导或间接由转录因子诱导盐胁迫相关基因的表达,最终植物体表现耐受胁迫、生长受阻或死亡.     

Phosphorelay and transcription control in cytokinin signal transduction

The past decade has seen substantial advances in knowledge of molecular mechanisms and actions of plant hormones, but only in the past few years has research on cytokinins begun to hit its stride. Cytokinins are master regulators of a large number of processes in plant development, which is known to be unusually plastic and adaptive, as well as resilient and perpetual. These characteristics allow plants to respond sensitively and quickly to their environments. Recent studies have demonstrated that cytokinin signaling involves a multistep two-component signaling pathway, resulting in the development of a canonical model of cytokinin signaling that is likely representative in plants. This Viewpoint outlines this general model, focusing on the specific example of Arabidopsis, and introduces the STKE Connections Maps for both the canonical module and the specific Arabidopsis Cytokinin Signaling Pathway.     

Glycosylphosphatidylinositol: a candidate system for interleukin-2 signal transduction

The mechanism of interleukin-2 (IL-2) signal transduction was analyzed by use of an inducible B lymphoma. Like normal antigen-activated B lymphocytes, the lymphoma cells respond to IL-2 by proliferating and differentiating into antibody-secreting cells; both responses are blocked by a second interleukin, IL-4. Analyses of the signaling pathway showed that IL-2 stimulated the rapid hydrolysis of an inositol-containing glycolipid to yield two possible second messengers, a myristylated diacylglycerol and an inositol phosphate-glycan. The myristylated diacylglycerol response exhibited the same IL-2 dose dependence as the growth and differentiative responses, and the generation of both hydrolysis products was inhibited by IL-4. These correlations implicate the glycosyl-phosphatidylinositol system in the intracellular relay of the IL-2 signal.     

植物氮磷营养的长距离信号转导

植物应对土壤多变的营养环境需整合和协调地上部和根系的养分感知信息,通过精细而复杂的信号转导机制,调控植物养分应答和生长发育进程。长距离信号转导机制的实现需经由维管系统进行信号分子的长距离运输(故称长距离信号)。在众多矿质营养元素中,氮和磷是限制植物生产力的主要元素。研究表明,蛋白质、小肽和microRNAs等多种分子均可作为长距离信号分子参与调控系统性氮磷信号转导。本文总结了目前鉴定到的氮磷营养长距离信号分子及相关信号转导机制,概述了光对氮磷长距离信号转导的影响,并对长距离信号未来研究方向进行了展望。     

植物激素的信号转导系统研究进展

植物激素是调节植物生长、发育和抗逆性的重要物质 .蛋白质激酶的磷酸化级联放大系统在激素的信号转导中起重要作用 .乙烯早期信号转导的 ETR1系统类似原核生物的信号转导的双组分系统 .本文综述了有关植物激素的信号转导系统的研究进展 ,并提出了今后研究的思路     

核黄素启动植物生长信号通路的初步研究

报道了核黄素促进植物生长的效应及分子反应。在实验室内对7种粮食、蔬菜和经济作物使用核黄素后，植物生长量增加23.8%-85.4%。在田间试验中，烟草使用核黄素后，生长量提高35.9%-108%。烤烟叶产量提高44.7%-110.3%。在拟南芥上，核黄素处理可以诱导PR-3b、PDF1.2、ETR1和EIN2基因的表达；PR-3b和PDF1.2是乙烯信号通路的分子标志，乙烯/茉莉酸信号传导可以调控植物生长发育；ETR1和EIN2是乙烯信号通路上，下游的关键调控基因，其产物分别作为乙烯的受体和转录调控因子起作用。根据以上这些结果，核黄素启动了植物生长信号传导通路的分子反应，促进了植物生长。     

Activated signal transduction kinases frequently occupy target genes

Cellular signal transduction pathways modify gene expression programs in response to changes in the environment, but the mechanisms by which these pathways regulate populations of genes under their control are not entirely understood. We present evidence that most mitogen-activated protein kinases and protein kinase A subunits become physically associated with the genes that they regulate in the yeast (Saccharomyces cerevisiae) genome. The ability to detect this interaction of signaling kinases with target genes can be used to more precisely and comprehensively map the regulatory circuitry that eukaryotic cells use to respond to their environment.     

乙烯在植物中的信号转导

乙烯是所有植物激素中结构最简单的一种,它对植物的代谢调节可贯串其整个生活周期.作为信号物质,它的生物合成主要由ACC合成酶和ACC氧化酶调控.通过对拟南芥中一系列乙烯反应的突变体的分析,人们掌握了很多在乙烯信号转导中发挥作用的生化组分.乙烯受体与细菌的双组分调节系统结构相似,乙烯与之结合后,调节与Raf激酶极为相似的CTR1,进而将信号传递给下游的EIN2.EIN3是一个转录因子,可结合到与乙烯反应相关的基因的启动子的特殊序列上,激活这些基因并使其转录,从而使植株出现与乙烯反应相关的诸多表型特征.     

昼夜节律调控拟南芥核黄素信号传导

植物昼夜节律钟对调控植物生理进程、环境响应和发育起着重要作用。与此相似,核黄素信号途径广泛参与调控植物生长与发育。研究结果表明:在野生型拟南芥叶片中,内源黄素含量(核黄素、FMN、FAD)在24 h周期内呈节律波动;RT-PCR分析表明,外源核黄素处理植株增强或抑制许多基因的表达,这些基因在野生型植株24 h内的表达水平也受昼夜节律调控;此外,外源核黄素能诱导植物产生防卫反应,该过程也受昼夜节律调控。因此得出结论:植物昼夜节律钟调控核黄素信号传导反应。     

Role of phosphatidylinositol kinase in PDGF receptor signal transduction

The molecules with which the platelet-derived growth factor (PDGF) receptor interacts to elicit the biochemical reactions responsible for cell proliferation have not been identified. Antisera directed against specific PDGF receptor peptides coprecipitated a phosphatidylinositol (PI) kinase and the PDGF receptor. Immunoprecipitates from PDGF-stimulated cells contained 10 to 50 times as much PI kinase as those from unstimulated cells. Mutation of the PDGF receptor by deletion of its kinase insert region resulted in a receptor markedly less effective than the wild type in eliciting cell proliferation and defective in PDGF-stimulated PI kinase, but still capable of PDGF-induced receptor autophosphorylation and phosphoinositide hydrolysis. These data show that the PDGF receptor is physically associated with a PDGF-sensitive PI kinase that is distinct from tyrosine kinase and is not required for PDGF-induced PI hydrolysis. The finding that the mutant PDGF receptor missing the kinase insert domain elicited known early biochemical responses to PDGF, but did not associate with or regulate PI kinase, suggests a novel role for the receptor-associated PI kinase in the transmission of mitogenic signals.     

Golf: an olfactory neuron specific-G protein involved in odorant signal transduction

Biochemical and electrophysiological studies suggest that odorants induce responses in olfactory sensory neurons via an adenylate cyclase cascade mediated by a G protein. An olfactory-specific guanosine triphosphate (GTP)-binding protein alpha subunit has now been characterized and evidence is presented suggesting that this G protein, termed Golf, mediates olfaction. Messenger RNA that encodes Golf alpha is expressed in olfactory neuroephithelium but not in six other tissues tested. Moreover, within the olfactory epithelium, Golf alpha appears to be expressed only by the sensory neurons. Specific antisera were used to localize Golf alpha protein to the sensory apparatus of the receptor neurons. Golf alpha shares extensive amino acid identity (88 percent) with the stimulatory G protein, Gs alpha. The expression of Golf alpha in S49 cyc- kin- cells, a line deficient in endogenous stimulatory G proteins, demonstrates its capacity to stimulate adenylate cyclase in a heterologous system.     

植物磷脂酶D对环境胁迫的响应和传导信号的功能

磷脂酶D(PLD)是一种分解磷脂的多功能酶。文章介绍了PLD的生化特性及其在信号转导中的作用,概述了PLD的调控机制及在机械损伤、低温、高渗透压、激素和微生物等环境胁迫下的响应。