Identification of scrapie prion protein-specific mRNA in scrapie-infected and uninfected brain

To date no nucleic acid has been found in the purified infectious agent which causes the spongiform encephalopathy known as scrapie. In an attempt to identify a unique scrapie virus-associated messenger RNA in tissues of infected animals, we have synthesized an oligonucleotide probe complementary to the mRNA sequence corresponding to the amino-acid sequence of the prion protein, PrP27-30 (ref. 1). We report here that, with this probe, a complementary DNA clone representing PrP27-30 was obtained from scrapie-infected mouse brain; the DNA sequence of this clone could be translated into a protein that matches exactly the published sequence of PrP27-30. The cDNA clone hybridized to a single 2.4-2.5-kilobase (kb) mRNA from both normal and scrapie-infected brain. Thus, the PrP27-30 mRNA is not uniquely associated with scrapie infectivity, suggesting that PrP27-30 may be a normal component of mouse and hamster brain.     

Cloning, sequencing and phylogenic analysis of duck prion gene

Duck prion gene was cloned and sequenced. Similar to mammalian prion protein (PrP), duck prion is encoded by a single exon of a single copy in genome, which was confirmed by Southern blot analysis. All of the structural features of mammalian PrP were also identified in the duck PrP. Compared with mammalian PrP, it exhibited a 30 % of general similarity. When compared with chicken PrP, it showed a higher homology of 97%. A phylogenetic tree was constructed to trace evolution of prion gene in animals.     

The most infectious prion protein particles

Neurodegenerative diseases such as Alzheimer's, Parkinson's and the transmissible spongiform encephalopathies (TSEs) are characterized by abnormal protein deposits, often with large amyloid fibrils. However, questions have arisen as to whether such fibrils or smaller subfibrillar oligomers are the prime causes of disease. Abnormal deposits in TSEs are rich in PrP(res), a protease-resistant form of the PrP protein with the ability to convert the normal, protease-sensitive form of the protein (PrP(sen)) into PrP(res) (ref. 3). TSEs can be transmitted between organisms by an enigmatic agent (prion) that contains PrP(res) (refs 4 and 5). To evaluate systematically the relationship between infectivity, converting activity and the size of various PrP(res)-containing aggregates, PrP(res) was partially disaggregated, fractionated by size and analysed by light scattering and non-denaturing gel electrophoresis. Our analyses revealed that with respect to PrP content, infectivity and converting activity peaked markedly in 17-27-nm (300-600 kDa) particles, whereas these activities were substantially lower in large fibrils and virtually absent in oligomers of < or =5 PrP molecules. These results suggest that non-fibrillar particles, with masses equivalent to 14-28 PrP molecules, are the most efficient initiators of TSE disease.     

Oligopeptide-repeat expansions modulate 'protein-only' inheritance in yeast.

The yeast [PSI+] element represents a new type of genetic inheritance, in which changes in phenotype are transmitted by a 'protein only' mechanism reminiscent of the 'protein-only' transmission of mammalian prion diseases. The underlying molecular mechanisms for both are poorly understood and it is not clear how similar they might be. Sup35, the [PSI+] protein determinant, and PrP, the mammalian prion determinant, have different functions, different cellular locations and no sequence similarity; however, each contains five imperfect oligopeptide repeats-PQGGYQQYN in Sup35 and PHGGGWGQ in PrP. Repeat expansions in PrP produce spontaneous prion diseases. Here we show that replacing the wild-type SUP35 gene with a repeat-expansion mutation induces new [PSI+] elements, the first mutation of its type among these newly described elements of inheritance. In vitro, fully denatured repeat-expansion peptides can adopt conformations rich in beta-sheets and form higher-order structures much more rapidly than wild-type peptides. Our results provide insight into the nature of the conformational changes underlying protein-based mechanisms of inheritance and suggest a link between this process and those producing neurodegenerative prion diseases in mammals.     

Sensitive detection of pathological prion protein by cyclic amplification of protein misfolding.

Prions are the infectious agents responsible for transmissible spongiform encephalopathies. The principal component of prions is the glycoprotein PrP(Sc), which is a conformationally modified isoform of a normal cell-surface protein called PrP(C) (ref. 1). During the time between infection and the appearance of the clinical symptoms, minute amounts of PrP(Sc) replicate by conversion of host PrP(C), generating large amounts of PrP(Sc) aggregates in the brains of diseased individuals. We aimed to reproduce this event in vitro. Here we report a procedure involving cyclic amplification of protein misfolding that allows a rapid conversion of large excess PrP(C) into a protease-resistant, PrP(Sc)-like form in the presence of minute quantities of PrP(Sc) template. In this procedure, conceptually analogous to polymerase chain reaction cycling, aggregates formed when PrP(Sc) is incubated with PrP(C) are disrupted by sonication to generate multiple smaller units for the continued formation of new PrP(Sc). After cyclic amplification more than 97% of the protease-resistant PrP present in the sample corresponds to newly converted protein. The method could be applied to diagnose the presence of currently undetectable prion infectious agent in tissues and biological fluids, and may provide a unique opportunity to determine whether PrP(Sc) replication results in the generation of infectivity in vitro.     

RNA molecules stimulate prion protein conversion

Much evidence supports the hypothesis that the infectious agents of prion diseases are devoid of nucleic acid, and instead are composed of a specific infectious protein. This protein, PrP(Sc), seems to be generated by template-induced conformational change of a normally expressed glycoprotein, PrP(C) (ref. 2). Although numerous studies have established the conversion of PrP(C) to PrP(Sc) as the central pathogenic event of prion disease, it is unknown whether cellular factors other than PrP(C) might be required to stimulate efficient PrP(Sc) production. We investigated the biochemical amplification of protease-resistant PrP(Sc)-like protein (PrPres) using a modified version of the protein-misfolding cyclic amplification method. Here we report that stoichiometric transformation of PrP(C) to PrPres in vitro requires specific RNA molecules. Notably, whereas mammalian RNA preparations stimulate in vitro amplification of PrPres, RNA preparations from invertebrate species do not. Our findings suggest that host-encoded stimulatory RNA molecules may have a role in the pathogenesis of prion disease. They also provide a practical approach to improve the sensitivity of diagnostic techniques based on PrPres amplification.     

Monoclonal antibodies inhibit prion replication and delay the development of prion disease

Prion diseases such as Creutzfeldt-Jakob disease (CJD) are fatal, neuro-degenerative disorders with no known therapy. A proportion of the UK population has been exposed to a bovine spongiform encephalopathy-like prion strain and are at risk of developing variant CJD. A hallmark of prion disease is the transformation of normal cellular prion protein (PrP(C)) into an infectious disease-associated isoform, PrP(Sc). Recent in vitro studies indicate that anti-PrP monoclonal antibodies with little or no affinity for PrP(Sc) can prevent the incorporation of PrP(C) into propagating prions. We therefore investigated in a murine scrapie model whether anti-PrP monoclonal antibodies show similar inhibitory effects on prion replication in vivo. We found that peripheral PrP(Sc) levels and prion infectivity were markedly reduced, even when the antibodies were first administered at the point of near maximal accumulation of PrP(Sc) in the spleen. Furthermore, animals in which the treatment was continued remained healthy for over 300 days after equivalent untreated animals had succumbed to the disease. These findings indicate that immunotherapeutic strategies for human prion diseases are worth pursuing.     

Linkage of a prion protein missense variant to Gerstmann-Str?ussler syndrome

Gerstmann-Str?ussler syndrome is a rare familial neurodegenerative condition that is vertically transmitted, in an apparently autosomal dominant way. It can also be horizontally transmitted to non-human primates and rodents through intracerebral inoculation of brain homogenates from patients with the disease. The exact incidence of the syndrome is unknown but is estimated to be between one and ten per hundred million. Patients initially suffer from ataxia or dementia and deteriorate until they die, in one to ten years. Protease-resistant prion protein (PrP) and PrP-immunoreactive amyloid plaques with characteristic morphology accumulate in the brains of these patients. Current diagnostic criteria for Gerstmann-Str?ussler syndrome incorporate clinical and neuropathological features, as animal transmission studies can be unreliable. PrP is implicated in the pathogenesis and transmission of the condition and in scrapie, an equivalent animal disease. It was discovered by enriching scrapie-infected hamster brain fractions for infectivity. Because there is compelling evidence that the scrapie isoform of PrP is a necessary component of the infectious particle, it seemed possible that the PrP gene on the short arm of human chromosome 20 in Gerstmann-Str?ussler syndrome might be abnormal. We show here that PrP codon 102 is linked to the putative gene for the syndrome in two pedigrees, providing the best evidence to date that this familial condition is inherited despite also being infectious, and that substitution of leucine for proline at PrP codon 102 may lead to the development of Gerstmann-Str?ussler syndrome.     

Transmissible and genetic prion diseases share a common pathway of neurodegeneration

Prion diseases can be infectious, sporadic and genetic. The infectious forms of these diseases, including bovine spongiform encephalopathy and Creutzfeldt-Jakob disease, are usually characterized by the accumulation in the brain of the transmissible pathogen, an abnormally folded isoform of the prion protein (PrP) termed PrPSc. However, certain inherited PrP mutations appear to cause neurodegeneration in the absence of PrPSc, working instead by favoured synthesis of CtmPrP, a transmembrane form of PrP. The relationship between the neurodegeneration seen in transmissible prion diseases involving PrPSc and that associated with ctmPrP has remained unclear. Here we find that the effectiveness of accumulated PrPSc in causing neurodegenerative disease depends upon the predilection of host-encoded PrP to be made in the ctmPrP form. Furthermore, the time course of PrPSc accumulation in transmissible prion disease is followed closely by increased generation of CtmPrP. Thus, the accumulation of PrPSc appears to modulate in trans the events involved in generating or metabolising CtmPrP. Together, these data suggest that the events of CtmPrP-mediated neurodegeneration may represent a common step in the pathogenesis of genetic and infectious prion diseases.     

Binding of disease-associated prion protein to plasminogen

Transmissible spongiform encephalopathies are associated with accumulation of PrP(Sc), a conformer of a cellular protein called PrP(C). PrP(Sc) is thought to replicate by imparting its conformation onto PrP(C) (ref. 1), yet conformational discrimination between PrP(C) and PrP(Sc) has remained elusive. Because deposition of PrP(Sc) alone is not enough to cause neuropathology, PrP(Sc) probably damages the brain by interacting with other cellular constituents. Here we find activities in human and mouse blood which bind PrP(Sc) and prion infectivity, but not PrP(C). We identify plasminogen, a pro-protease implicated in neuronal excitotoxicity, as a PrP(Sc)-binding protein. Binding is abolished if the conformation of PrP(Sc) is disrupted by 6M urea or guanidine. The isolated lysine binding site 1 of plasminogen (kringles I-III) retains this binding activity, and binding can be competed for with lysine. Therefore, plasminogen represents the first endogenous factor discriminating between normal and pathological prion protein. This unexpected property may be exploited for diagnostic purposes.     

Atomic structures of amyloid cross-beta spines reveal varied steric zippers

Amyloid fibrils formed from different proteins, each associated with a particular disease, contain a common cross-beta spine. The atomic architecture of a spine, from the fibril-forming segment GNNQQNY of the yeast prion protein Sup35, was recently revealed by X-ray microcrystallography. It is a pair of beta-sheets, with the facing side chains of the two sheets interdigitated in a dry 'steric zipper'. Here we report some 30 other segments from fibril-forming proteins that form amyloid-like fibrils, microcrystals, or usually both. These include segments from the Alzheimer's amyloid-beta and tau proteins, the PrP prion protein, insulin, islet amyloid polypeptide (IAPP), lysozyme, myoglobin, alpha-synuclein and beta(2)-microglobulin, suggesting that common structural features are shared by amyloid diseases at the molecular level. Structures of 13 of these microcrystals all reveal steric zippers, but with variations that expand the range of atomic architectures for amyloid-like fibrils and offer an atomic-level hypothesis for the basis of prion strains.     

Evidence for oxidative damage to prion protein in prion diseases

In prion diseases the irreversible protein structural transformation process is completed in the brains of mammals within a few months, the uniformly generated infectivity displays extraordinary resistance to inactivation, suggesting that a vital energy source is required for the production of infectious particles. Considering the high oxygen-respiration rate in the brains, prion protein oxidative damage can be the crucial factor. Both theoretical consideration of the nature of protein radical reactions and a large body of previously unraveled feature of scrapie and prion diseases have provided multiple distinct lines of compelling evidence which persuasively support a suggestion that the infectious agents may be prion (free) radicals produced from protein oxidative damage. This paper describes that scrapie prions are most likely formed from prion radicals and oxidative species-mediated sequence-specific cross-linking of benign prion proteins.     

Influence of PrP 106―126 on expression of laminin and fibronectin in astrocyte

Astrogliosis is a hallmark of prion disease, but the metabolic alterations of astrocytes remain poorly documented. A synthetic peptide corresponding to amino acid 106-126 of the human prion protein （PrP） has been shown to be toxic to neurons. In this study, the effects of PrP 106-126 on astrocytes were investigated in vitro. The proliferation of astrocytes was significantly （P 〈 0.05） increased when grown in media conditioned with PrP 106-126 （80 μmol/L） from microglia. The expression of laminin （LN） and fibronectin （FN） was examined at both mRNA and protein levels. The results showed that exposure of astrocytes to PrP 106-126 enhanced the expression of LN and FN. The increase of FN in astrocyte cultures required cytokines previously released by activated microglia. This study reveals the expression of LN and FN affected by PrP106-126.     

Prion propagation and toxicity in vivo occur in two distinct mechanistic phases

Mammalian prions cause fatal neurodegenerative conditions including Creutzfeldt-Jakob disease in humans and scrapie and bovine spongiform encephalopathy in animals. Prion infections are typically associated with remarkably prolonged but highly consistent incubation periods followed by a rapid clinical phase. The relationship between prion propagation, generation of neurotoxic species and clinical onset has remained obscure. Prion incubation periods in experimental animals are known to vary inversely with expression level of cellular prion protein. Here we demonstrate that prion propagation in brain proceeds via two distinct phases: a clinically silent exponential phase not rate-limited by prion protein concentration which rapidly reaches a maximal prion titre, followed by a distinct switch to a plateau phase. The latter determines time to clinical onset in a manner inversely proportional to prion protein concentration. These findings demonstrate an uncoupling of infectivity and toxicity. We suggest that prions themselves are not neurotoxic but catalyse the formation of such species from PrP(C). Production of neurotoxic species is triggered when prion propagation saturates, leading to a switch from autocatalytic production of infectivity (phase 1) to a toxic (phase 2) pathway.     

Prions and their partners in crime

Prions, the infectious agents of transmissible spongiform encephalopathies (TSEs), have defied full characterization for decades. The dogma has been that prions lack nucleic acids and are composed of a pathological, self-inducing form of the host's prion protein (PrP). Recent progress in propagating TSE infectivity in cell-free systems has effectively ruled out the involvement of foreign nucleic acids. However, host-derived nucleic acids or other non-PrP molecules seem to be crucial. Interactions between TSE-associated PrP and its normal counterpart are also pathologically important, so the physiological functions of normal PrP and how they might be corrupted by TSE infections have been the subject of recent research.     

西瓜花叶病毒HC-Pro基因的克隆与原核表达

利用RT-PCR方法获得了西瓜花叶病毒(WMV)陕西分离物HC-Pro基因,大小为1 371 bp.将HC-Pro基因克隆到pMD18-T Simple Vector,测序分析发现与其它国家HC-Pro核苷酸同源性为90.7%~94.8%.将HC-Pro基因定向插入EcoR I/Sal I切开的pET30a中,构建了原核表达载体pET30-WHC,转化大肠杆菌BL21.经IPTG诱导2~8 h后,成功表达了分子量约为57 kD的HC-Pro蛋白.通过不同时间诱导发现,加入IPTG 2 h后蛋白开始表达,继续诱导到8h后表达量变化不大.以诱导的蛋白为抗原免疫家兔,制备了HC-Pro蛋白的抗血清,ELISA法测其效价为1/6 400,Western blot分析能与HC-Pro发生血清学反应.     

Normal development and behaviour of mice lacking the neuronal cell-surface PrP protein.

PrPC is a host protein anchored to the outer surface of neurons and to a lesser extent of lymphocytes and other cells. The transmissible agent (prion) responsible for scrapie is believed to be a modified form of PrPC. Mice homozygous for disrupted PrP genes have been generated. Surprisingly, they develop and behave normally for at least seven months, and no immunological defects are apparent. It is now feasible to determine whether mice devoid of PrPC can propagate prions and are susceptible to scrapie pathogenesis.     

Daxx-C抗血清的制备与纯化及初步应用

将含有Daxx-C端的融合蛋白6His-DM626-740纯化物免疫小鼠,分析抗血清效价并将其纯化,为进一步分析Daxx在人乳头瘤病毒16型(HPV16)阳性宫颈癌组织中的分布奠定基础。将6His-DM626-740纯化物以皮下多点注射和腹腔注射方式免疫接种4只8周龄雌性BALB/c小鼠,初次免疫3周后,加强免疫1次,以后每周加强免疫1次;共免疫4次。每次免疫前及末次免疫后7天取血,ELISA测定抗体效价。饱和硫酸铵盐析沉淀法初步纯化抗血清,并用Western blot检测之。培养Caski细胞,利用间接免疫荧光试验观察Daxx在细胞中的分布与定位。纯化物免疫小鼠后,制备的Daxx-C多克隆抗体效价为1:6400。纯化的抗血清能够与IPTG诱导表达的6His-DM626-740及其纯化物发生结合反应。在Caski细胞,显绿色信号的Daxx主要分布于胞浆,少数分布于胞核且在核膜附近荧光较强,呈区域性聚集。6His-DM626-740纯化物具有良好的免疫原性;纯化的抗血清可用来检测细胞中的Daxx。     

新基因Splt137在大肠杆菌中的表达及抗体制备

用PCR的方法扩增得到斜纹夜蛾核多角体病毒 (SpltMNPV)ORF137全长基因 (Splt137)。将其克隆到原核表达载体pQE30上 ,并转化大肠杆菌M15 ,在IPTG诱导下表达了与预期相对分子质量相符的一个 2 7× 10 7的蛋白质 ,经过聚丙烯酰氨凝胶电泳纯化 ,免疫家兔制备了抗Splt137抗体。Western免疫印迹分析表明 ,该抗体适合用作Splt137蛋白的进一步分析。     

Protein-only transmission of three yeast prion strains

Key questions regarding the molecular nature of prions are how different prion strains can be propagated by the same protein and whether they are only protein. Here we demonstrate the protein-only nature of prion strains in a yeast model, the [PSI] genetic element that enhances the read-through of nonsense mutations in the yeast Saccharomyces cerevisiae. Infectious fibrous aggregates containing a Sup35 prion-determining amino-terminal fragment labelled with green fluorescent protein were purified from yeast harbouring distinctive prion strains. Using the infectious aggregates as 'seeds', elongated fibres were generated in vitro from the bacterially expressed labelled prion protein. De novo generation of strain-specific [PSI] infectivity was demonstrated by introducing sheared fibres into uninfected yeast hosts. The cross-sectional morphology of the elongated fibres generated in vitro was indistinguishable from that of the short yeast seeds, as visualized by electron microscopy. Electron diffraction of the long fibres showed the 4.7 A spacing characteristic of the cross-beta structure of amyloids. The fact that the amyloid fibres nucleated in vitro propagate the strain-specific infectivity of the yeast seeds implies that the heritable information of distinct prion strains must be encoded by different, self-propagating cross-beta folding patterns of the same prion protein.