酵母朊病毒的遗传与增殖

１９８２年,Ｐｒｕｓｉｎｅｒ等发现,在感染瘙痒病的仓鼠脑中有一种异常蛋白,名其为“蛋白质感染颗粒”（ｐｒｏｔｅｉｎａｃｅｏｕｓｉｎｆｅｃｔｉｏｕｓｐａｒｔｉ－ｃｌｅ）。Ｐｒｕｓｉｎｅｒ用ｐｒｉｏｎ（现译为朊病毒）这一名词把这类病原体与病毒、细菌、真菌以及其它已知的病原体区分开。后来发现这种蛋白质能够自我催化复制,且有两种构象,即正常态的ＰｒＰＣ和感染态的ＰｒＰＳＣ。两者的化学性质也不同：ＰｒＰＣ能溶于非变性洗涤剂而ＰｒＰＳＣ不溶;ＰｒＰＣ易被蛋白酶消化而ＰｒＰＳＣ则具部分抗性。在酵母中,朊病毒不…     

乳酸克鲁维酵母表达外源蛋白研究进展

乳酸克鲁维酵母已成功地应用于多种异源蛋白的表达生产之中。与其他酵母相比，乳酸克鲁维酵母具有许多优点，如超强的分泌能力，良好的大规模发酵特性、食品安全的级别及整合表达能力等，其作为宿主系统表达药用蛋白也已显示出巨大的潜力。从不同的菌属、遗传工程和分子生物学技术（如启动子、表达载体）等方面简要综述了乳酸克鲁维酵母作为蛋白表达宿主系统的优势。     

Non-targeted Identification of Prions and Amyloid-forming Proteins from Yeast and Mammalian Cells

The formation of amyloid aggregates is implicated both as a primary cause of cellular degeneration in multiple human diseases and as a functional mechanism for providing extraordinary strength to large protein assemblies. The recent identification and characterization of several amyloid proteins from diverse organisms argues that the amyloid phenomenon is widespread in nature. Yet identifying new amyloid-forming proteins usually requires a priori knowledge of specific candidates. Amyloid fibers can resist heat, pressure, proteolysis, and denaturation by reagents such as urea or sodium dodecyl sulfate. Here we show that these properties can be exploited to identify naturally occurring amyloid-forming proteins directly from cell lysates. This proteomic-based approach utilizes a novel purification of amyloid aggregates followed by identification by mass spectrometry without the requirement for special genetic tools. We have validated this technique by blind identification of three amyloid-based yeast prions from laboratory and wild strains and disease-related polyglutamine proteins expressed in both yeast and mammalian cells. Furthermore, we found that polyglutamine aggregates specifically recruit some stress granule components, revealing a possible mechanism of toxicity. Therefore, core amyloid-forming proteins as well as strongly associated proteins can be identified directly from cells of diverse origin.     

Yeast Prions: Evolution of the Prion Concept

Prions (infectious proteins) analogous to the scrapie agent have been identified in Saccharomyces cerevisiae and Podospora anserina based on their special genetic characteristics. Each is a protein acting as a gene, much like nucleic acids have been shown to act as enzymes. The [URE3], [PSI⁺], [PIN⁺] and [Het-s] prions are self-propagating amyloids of Ure2p, Sup35p, Rnq1p and the HET-s protein, respectively. The [β] and [C] prions are enzymes whose precursor activation requires their own active form. [URE3] and [PSI⁺] are clearly diseases, while [Het-s] and [β] carry out normal cell functions. Surprisingly, the prion domains of Ure2p and Sup35p can be randomized without loss of ability to become a prion. Thus amino acid content and not sequence determine these prions. Shuffleability also suggests amyloids with a parallel in-register β-sheet structure.Key Words: Ure2, Sup35, Rnq1, HETs, PrP, prion, amyloid     

Mouse Models for Studying the Formation and Propagation of Prions

Prions are self-propagating protein conformers that cause a variety of neurodegenerative disorders in humans and animals. Mouse models have played key roles in deciphering the biology of prions and in assessing candidate therapeutics. The development of transgenic mice that form prions spontaneously in the brain has advanced our understanding of sporadic and genetic prion diseases. Furthermore, the realization that many proteins can become prions has necessitated the development of mouse models for assessing the potential transmissibility of common neurodegenerative diseases. As the universe of prion diseases continues to expand, mouse models will remain crucial for interrogating these devastating illnesses.     

Secretion of Recombinant Proteins via the Chaperone/Usher Pathway in Escherichia coli

F1 antigen (Caf1) of Yersinia pestis is assembled via the Caf1M chaperone/Caf1A usher pathway. We investigated the ability of this assembly system to facilitate secretion of full-length heterologous proteins fused to the Caf1 subunit in Escherichia coli. Despite correct processing of a chimeric protein composed of a modified Caf1 signal peptide, mature human interleukin-1β (hIL-1β), and mature Caf1, the processed product (hIL-1β:Caf1) remained insoluble. Coexpression of this chimera with a functional Caf1M chaperone led to the accumulation of soluble hIL-1β:Caf1 in the periplasm. Soluble hIL-1β:Caf1 reacted with monoclonal antibodies directed against structural epitopes of hIL-1β. The results indicate that Caf1M-induced release of hIL-1β:Caf1 from the inner membrane promotes folding of the hIL-1β domain. Similar results were obtained with the fusion of Caf1 to hIL-1β receptor antagonist or to human granulocyte-macrophage colony-stimulating factor. Following coexpression of the hIL-1β:Caf1 precursor with both the Caf1M chaperone and Caf1A outer membrane protein, hIL-1β:Caf1 could be detected on the cell surface of E. coli. These results demonstrate for the first time the potential application of the chaperone/usher secretion pathway in the transport of subunits with large heterogeneous N-terminal fusions. This represents a novel means for the delivery of correctly folded heterologous proteins to the periplasm and cell surface as either polymers or cleavable monomeric domains.     

Regulation of Chaperone Effects on a Yeast Prion by Cochaperone Sgt2

Yeast prions, based on self-seeded highly ordered fibrous aggregates (amyloids), serve as a model for human amyloid diseases. Propagation of yeast prions depends on the balance between chaperones of the Hsp100 and Hsp70 families. The yeast prion [PSI⁺] can be eliminated by an excess of the chaperone Hsp104. This effect is reversed by an excess of the chaperone Hsp70-Ssa. Here we show that the actions of Hsp104 and Ssa on [PSI⁺] are modulated by the small glutamine-rich tetratricopeptide cochaperone Sgt2. Sgt2 is conserved from yeast to humans, has previously been implicated in the guided entry of tail-anchored proteins (GET) trafficking pathway, and is known to interact with Hsps, cytosolic Get proteins, and tail-anchored proteins. We demonstrate that Sgt2 increases the ability of excess Ssa to counteract [PSI⁺] curing by excess Hsp104. Deletion of SGT2 also restores trafficking of a tail-anchored protein in cells with a disrupted GET pathway. One region of Sgt2 interacts both with the prion domain of Sup35 and with tail-anchored proteins. Sgt2 levels are increased in response to the presence of a prion when major Hsps are not induced. Our data implicate Sgt2 as an amyloid “sensor” and a regulator of chaperone targeting to different types of aggregation-prone proteins.     

Heterologous Expression and Subcellular Localization of Pumpkin Seed Tonoplast Intrinsic Proteins (TIP) in Yeast Cells

Two tonoplast intrinsic proteins (TIP) of pumpkin seeds, pMP23and MP28, were expressed in yeast cells under control of theGAL1 promoter, and the subcellular localization of the proteinswas analyzed. The pMP23 and MP28 stably accumulated in the yeastvacuolar membrane when the proteins were expressed in the proteinaseA-deficient strain (pep4), which lacks the activities of vacuolarproteases. However, pMP23 and MP28 did not accumulate in thewild-type strain; the expressed pMP23 and MP28 were degradedin a proteinase A-dependent manner. These results indicate thatpMP23 and MP28 are transported to the vacuolar membrane whenexpressed in yeast. ⁵Present address: Department of Biochemistry and Molecular Biology,The Pennsylvania State University, University Park, PA16802,U.S.A.     

Direct Observation of the Uptake of Outer Membrane Proteins by the Periplasmic Chaperone Skp

The transportation of membrane proteins through the aqueous subcellular space is an important and challenging process. Its molecular mechanism and the associated structural change are poorly understood. Periplasmic chaperones, such as Skp in Escherichia coli, play key roles in the transportation and protection of outer membrane proteins (OMPs) in Gram-negative bacteria. The molecular mechanism through which Skp interacts with and protects OMPs remains mysterious. Here, a combined experimental and molecular dynamics simulation study was performed to gain the structural and dynamical information in the process of OMPs and Skp binding. Stopped-flow experiments on site specific mutated and labeled Skp and several OMPs, namely OmpC, the transmembrane domain of OmpA, and OmpF, allowed us to obtain the mechanism of OMP entering the Skp cavity, and molecular dynamics simulations yielded detailed molecular interactions responsible for this process. Both experiment and simulation show that the entrance of OMP into Skp is a highly directional process, which is initiated by the interaction between the N-terminus of OMP and the bottom “tentacle” domain of Skp. The opening of the more flexible tentacle of Skp, the non-specific electrostatic interactions between OMP and Skp, and the constant formation and breaking of salt bridges between Skp and its substrate together allow OMP to enter Skp and gradually “climb” into the Skp cavity in the absence of an external energy supply.     

枯草芽胞杆菌孢子表面展示外源蛋白的研究

枯草芽胞杆菌孢子表面展示技术是最近十几年新兴的一种外源蛋白固定方法,已在酶学、疫苗学、靶向药物制备、金属污染治理等领域获得了广泛应用。以孢子衣壳蛋白为载体蛋白,已经成功地把许多抗原、酶和其他蛋白展示在孢子外表面。枯草芽胞杆菌孢子衣壳由多种衣壳蛋白组成,但可用做载体蛋白的并不多,且它们的特性不同。综合介绍了枯草芽胞杆菌孢子表面展示外源蛋白这种新型技术的具体机理,及其在国内外各领域应用的研究进展。     

The Yeast AAA+ Chaperone Hsp104 Is Part of a Network That Links the Actin Cytoskeleton with the Inheritance of Damaged Proteins

The yeast AAA⁺ chaperone Hsp104 is essential for the development of thermotolerance and for the inheritance of prions. Recently, Hsp104, together with the actin cytoskeleton, has been implicated in the asymmetric distribution of carbonylated proteins. Here, we investigated the interplay between Hsp104 and actin by using a dominant-negative variant of Hsp104 (HAP/ClpP) that degrades substrate proteins instead of remodeling them. Coexpression of HAP/ClpP causes defects in morphology and the actin cytoskeleton. Taking a candidate approach, we identified Spa2, a member of the polarisome complex, as an Hsp104 substrate. Furthermore, we provided genetic evidence that links Spa2 and Hsp104 to Hof1, a member of the cytokinesis machinery. Spa2 and Hof1 knockout cells are affected in the asymmetric distribution of damaged proteins, suggesting that Hsp104, Spa2, and Hof1 are members of a network controlling the inheritance of carbonylated proteins.The ensemble of molecular chaperones and proteases constitutes the cellular system that repairs and eliminates misfolded proteins. The activity of this system ensures not only the recovery of cells from protein-damaging stress conditions, but also the maintenance of protein homeostasis under normal growth conditions. The concomitant involvement of members of the Hsp70 and Hsp90 chaperone families in stress-related, regulatory, and housekeeping functions allows the integration of environmental stimuli into regulatory networks (4, 24, 39, 40). However, it has remained unclear whether other chaperones are also involved in regulatory processes.One chaperone which so far has been connected only to stress-related protein quality functions is the oligomeric AAA⁺ chaperone Hsp104 of Saccharomyces cerevisiae. Hsp104 is essential for the development of thermotolerance by reactivating aggregated proteins after severe stress conditions and for prion propagation by severing prion fibrils (31). Yeast cells, when grown at 30°C, harbor approximately 5,000 copies of Hsp104 hexamers per cell, a number that is minor compared to other cytosolic chaperone machineries (e.g., Hsp70 and Hsp90) that are involved in general protein-folding events (10). The known cellular functions of Hsp104, however, cannot provide a rationale for the determined Hsp104 levels, since protein aggregation is hardly detectable in yeast cells at 30°C even in mutant cells lacking Hsp104 function. Furthermore, yeast prions occur de novo at a very low rate of 10⁻⁶ per cell. In consequence, both well-characterized Hsp104 activities are barely required at 30°C, suggesting that Hsp104 has additional, so far unknown housekeeping functions. On the other hand, an S. cerevisiae hsp104 knockout exhibits no obvious phenotype at 30°C (27), giving no clues to a potential involvement of Hsp104 in other cellular processes.Recently, Hsp104 was demonstrated to influence the asymmetric distribution of oxidatively damaged (carbonylated) proteins (8). It remained unclear whether the role of Hsp104 in this process relies on its known activities in protein quality control or on an unknown involvement in other cellular processes. Here, we provide evidence that Hsp104 is part of a network that controls the inheritance of damaged proteins under physiological growth conditions.     

异源表达脂肪酶的重组酵母筛选培养基的改良

在脂肪酶产生菌的筛选中,最常用的方法是三丁酸甘油酯琼脂平板透明圈法和橄榄油琼脂平板变色圈法。而传统的三丁酸甘油酯平板缺乏有效营养成分,重组酵母无法生长;橄榄油平板灵敏度较低,低脂肪酶活力的重组酵母不能产生变色圈,这给产脂肪酶基因工程菌的鉴定带来了困难。本研究在三丁酸甘油酯平板的基础上,添加适合酵母生长的营养成分,获得了新的改良培养基;重组酵母在该培养基上生长良好、水解圈清晰,检测脂肪酶灵敏度高。     

OsPDR在酵母中异源表达增强了酵母对钴的耐受性

在通过RNA-Seq技术得到的镉响应转录组图谱中,用50 μmol/L Cd处理24 h后,一个镉响应金属离子转运蛋白OsPDR被鉴定出其在水稻(Oryza sativa ssp. japonica cv. Nipponbare)茎中的表达量显著上调．本研究中,从水稻(Oryza sativa cv. Nipponbare)中分离了OsPDR基因,并对其金属离子转移活性进行了分析．金属耐受性实验结果表明,过表达OsPDR能提高酵母对Co的耐受性,但对Zn、Ni和Cd的耐受性不强,并且经电感耦合等离子体质谱法(ICP-MS)测定Co含量后,与空载体转化酵母相比,过表达OsPDR的酵母中Co的积累更高．利用共聚焦显微镜观察发现,EGFP-OsPDR融合蛋白定位于液泡膜上．这些数据表明OsPDR可能在Co稳态中起着重要作用．OsPDR在植物中的作用,还需要进一步的研究．     

Yeast two-hybrid方法筛选VISA相互作用蛋白

病原微生物感染对人类健康构成巨大威胁,先天免疫系统是生物体在长期进化过程中建立起来的天然保护系统。VISA(MAVS,CARDIF,IPS-1[1-3])是连接胞浆dsRNA受体RIG-I与下游信号转导通路的一个接头蛋白,研究结果表明VISA无论在TLR3非依赖的或者TLR3介导的抗病毒IFN信号途径中都具有关键作用,但目前对VISA信号转导的详细机制还不十分清楚。更多VISA相互作用蛋白的发现以及它们之间的作用机制的研究能完善我们对VISA参与的信号转导机制的认识。利用酵母双杂交系统,用VISA蛋白的全长做诱饵(Bait)筛选293 T细胞c DNA表达文库,并结合免疫共沉淀实验,双荧光素酶报告基因系统验证筛选到的阳性克隆和VISA作用的真实性。通过酵母双杂交系统成功筛选到Sec13L1候选基因并验证了其与VISA的全长蛋白相互作用,在293 T细胞中过表达该基因,研究结果显示Sec13L1过表达能促进VISA对IFNβ的诱导,并存在剂量效应。     

Suppressing Posttranslational Gluconoylation of Heterologous Proteins by Metabolic Engineering of Escherichia coli

Minimization of chemical modifications during the production of proteins for pharmaceutical and medical applications is of fundamental and practical importance. The gluconoylation of heterologously expressed protein which is observed in Escherichia coli BL21(DE3) constitutes one such undesired posttranslational modification. We postulated that formation of gluconoylated/phosphogluconoylated products of heterologous proteins is caused by the accumulation of 6-phosphogluconolactone due to the absence of phosphogluconolactonase (PGL) in the pentose phosphate pathway. The results obtained demonstrate that overexpression of a heterologous PGL in BL21(DE3) suppresses the formation of the gluconoylated adducts in the therapeutic proteins studied. When this E. coli strain was grown in high-cell-density fed-batch cultures with an extra copy of the pgl gene, we found that the biomass yield and specific productivity of a heterologous 18-kDa protein increased simultaneously by 50 and 60%, respectively. The higher level of PGL expression allowed E. coli strain BL21(DE3) to satisfy the extra demand for precursors, as well as the energy requirements, in order to replicate plasmid DNA and express heterologous genes, as metabolic flux analysis showed by the higher precursor and NADPH fluxes through the oxidative branch of the pentose phosphate shunt. This work shows that E. coli strain BL21(DE3) can be used as a host to produce three different proteins, a heterodimer of liver X receptors, elongin C, and an 18-kDa protein. This is the first report describing a novel and general strategy for suppressing this nonenzymatic modification by metabolic pathway engineering.     

Modulation of Chaperone Gene Expression in Mutagenized Saccharomyces cerevisiae Strains Developed for Recombinant Human Albumin Production Results in Increased Production of Multiple Heterologous Proteins

The yeast Saccharomyces cerevisiae has been successfully established as a commercially viable system for the production of recombinant proteins. Manipulation of chaperone gene expression has been utilized extensively to increase recombinant protein production from S. cerevisiae, focusing predominantly on the products of the protein disulfide isomerase gene PDI1 and the hsp70 gene KAR2. Here we show that the expression of the genes SIL1, LHS1, JEM1, and SCJ1, all of which are involved in regulating the ATPase cycle of Kar2p, is increased in a proprietary yeast strain, developed by several rounds of random mutagenesis and screening for increased production of recombinant human albumin (rHA). To establish whether this expression contributes to the enhanced-production phenotype, these genes were overexpressed both individually and in combination. The resultant strains showed significantly increased shake-flask production levels of rHA, granulocyte-macrophage colony-stimulating factor, and recombinant human transferrin.     

Stepwise Splitting of Ribosomal Proteins from Yeast Ribosomes by LiCl

Structural studies have revealed that the core of the ribosome structure is conserved among ribosomes of all kingdoms. Kingdom-specific ribosomal proteins (r-proteins) are located in peripheral parts of the ribosome. In this work, the interactions between rRNA and r-proteins of eukaryote Saccharomyces cerevisiae ribosome were investigated applying LiCl induced splitting and quantitative mass spectrometry. R-proteins were divided into four groups according to their binding properties to the rRNA. Most yeast r-proteins are removed from rRNA by 0.5–1 M LiCl. Eukaryote-specific r-proteins are among the first to dissociate. The majority of the strong binders are known to be required for the early ribosome assembly events. As compared to the bacterial ribosome, yeast r-proteins are dissociated from rRNA at lower ionic strength. Our results demonstrate that the nature of protein-RNA interactions in the ribosome is not conserved between different kingdoms.     

应用酵母双杂交系统筛选AMPK相互作用蛋白

一磷酸腺苷激活蛋白激酶(AMPK)是调节体内代谢平衡的丝氨酸/苏氨酸蛋白激酶。应用酵母双杂交系统,以AMPKβ1亚基作为"诱饵"蛋白,筛选均一化的人源cDNA文库,寻找与AMPK相互作用的蛋白。通过对150个阳性克隆进行验证,最终得到了63个与AMPKβ1亚基相互作用的蛋白。其中,包括代谢酶、转录因子或转录相关蛋白、蛋白转运相关蛋白、GTP结合蛋白、支架蛋白、细胞周期调节蛋白、RNA结合蛋白等以及一些未知功能的蛋白。从酵母双杂交的结果来看,AMPK不仅在代谢领域,而且在许多非代谢领域,如核受体及其它转录因子的调节、信号转导、DNA修复及细胞周期调节等,可能都起到非常重要的作用。