Comparison of tuberculin activity using the interferon-gamma assay for the diagnosis of bovine tuberculosis

In this study, interferon-gamma (IFN-gamma) responses in whole blood cultures stimulated with tuberculins from different sources were compared with regard to their diagnostic reliability in cattle experimentally and naturally infected with Mycobacterium bovis. The IFN-gamma responses to different concentrations of purified protein derivatives (PPDs) from M bovis and Mycobacterium avium were quantified. Significant differences (P<0.05) between sources and concentrations of PPDs used for stimulation were detected, indicating a need for standardisation of PPDs used in the IFN-gamma assay. Additionally, a tool named'relative potency 30' that allows rapid comparison of batches and sources of PPDs was defined.

Bovine tuberculosis: a review of current and emerging diagnostic techniques in view of their relevance for disease control and eradication

Existing strategies for long-term bovine tuberculosis (bTB) control/eradication campaigns are being reconsidered in many countries because of the development of new testing technologies, increased global trade, continued struggle with wildlife reservoirs of bTB, redistribution of international trading partners/agreements, and emerging financial and animal welfare constraints on herd depopulation. Changes under consideration or newly implemented include additional control measures to limit risks with imported animals, enhanced programs to mitigate wildlife reservoir risks, re-evaluation of options to manage bTB-affected herds/regions, modernization of regulatory framework(s) to re-focus control efforts, and consideration of emerging testing technologies (i.e. improved or new tests) for use in bTB control/eradication programs. Traditional slaughter surveillance and test/removal strategies will likely be augmented by incorporation of new technologies and more targeted control efforts. The present review provides an overview of current and emerging bTB testing strategies/tools and a vision for incorporation of emerging technologies into the current control/eradication programs.

Applicability of a rapid chromatographic immunoassay for analysis of the distribution of PrPBSE in confirmed BSE cases

The Prionics-Check PrioSTRIP is a rapid chromatographic immunoassay for bovine spongiform encephalopathy (BSE) approved by the European Union in 2004. In this study, the PrioSTRIP was used to analyse PrP(BSE) in 16 different brain areas of nine confirmed BSE cases. The levels of PrP(BSE) in the different brain areas were plotted to give the brain PrP(BSE) distribution curve (BPDC) and compared with the BPDC obtained previously by Western blotting and enzyme-linked immunosorbent assay (ELISA) methods on the same samples. The distribution of PrP(BSE) in different areas of the brain was similar, irrespective of the test applied, indicating that each test could be used for the characterisation of BSE cases.

Search for a scrapie-specific nucleic acid: a progress report

Scrapie agent contains a proteinaceous component as well as an 'informational' molecule (suggested by the existence of distinct strains of scrapie). These operationally defined entities may be the same molecule, an infectious protein, or distinct, in which case a nucleic acid might encode the genetic information. Purification of scrapie agent enriched a protein, PrPSc, by virtue of its relative protease resistance. There is only a single PrP gene and the primary translation product of PrP mRNA is the same in normal and scrapie-infected brain; therefore the normal PrPC and the protease-resistant isoform, PrPSc, found in scrapie, probably result from different post-translational events. To search for scrapie-specific nucleic acid, globin RNA made in vitro was added to highly purified infectious preparations at a ratio of 10(3) molecules per infectious unit, nucleic acids were isolated and denatured, and cDNA synthesized using random oligonucleotide primers. Clones containing globin-related sequences were identified by in situ hybridization. 150 plaques not hybridizing to the globin probe were isolated. Inserts larger than 50 base pairs were analysed. By hybridization to a globin probe at reduced stringency all but four clones were found to contain small globin related inserts; two of these hybridized to hamster repetitive sequences as shown by Southern blot analysis. The other clones not related to hamster nucleic acids may be derived from unknown sources of contamination or from scrapie-specific nucleic acids.

Diagnostics for TSE agents

Bovine Spongiform Encephalopathy (BSE) is a fatal acquired neuro-degenerative disease in cattle, belonging to the group of transmissible spongiform encephalopathies (TSEs) or prion diseases. Since its first recognition in the U.K. in 1986, BSE has raised great public health concerns because the BSE agent has been shown to cause variant Creutzfeldt Jakob Disease (vCJD) in humans. With the introduction of mandatory active surveillance programmes in the European Union the need to develop rapid tests to diagnose BSE has become a high priority. Up to now, the European Union has approved twelve rapid tests for BSE monitoring in cattle, and approval for two new tests which have been evaluated in 2004 is pending. These rapid screening tests have been used in active surveillance of BSE and have greatly improved the detection of infected cattle before their entry into the human food chain. At present, no diagnostic test exists for the detection of prions in live animals or humans. New diagnostic techniques aimed at increasing the sensitivity and specificity of PrPsc detection in body fluids and at identifying novel surrogate markers are under development.

Comparative study of the PrPBSE distribution in brains from BSE field cases using rapid tests

The distribution of PrP(BSE) in the brain of nine confirmed BSE field cases was analyzed using immunohistochemistry and compared to the levels of PrP(BSE) determined by two rapid tests (Prionics-Check WESTERN and Prionics-Check LIA). Each brain was dissected into 16 areas: spinal cord, medulla oblongata, pons, mesencephalon, thalamus, hippocampus, cerebellar vermis, cerebellar medulla, cerebellar hemispheres, occipital cortex, temporal cortex, parietal cortex, striatum, frontal cortex, piriform lobe and olfactory bulbs. The highest levels of PrP(BSE) were detected in the medulla oblongata, spinal cord and pons, and correspondingly both rapid tests showed 100% correlation with the immunohistochemistry with regard to sensitivity and specificity. Some inconsistencies between the levels of PrP(BSE) determined either by immunohistochemistry or by the rapid tests were found in brain areas with medium to low levels of PrP(BSE). These brain areas included the cerebellar hemisphere, olfactory bulb, and the temporal and parietal cortices. A brain PrP(BSE) distribution curve (BPDC) was designed by plotting the PrP(BSE) signals obtained from the two rapid tests versus the anatomical region along the caudal-rostral axis of the brain. Comparison of the BPDC of the nine BSE cases showed that all cases had a similar PrP(BSE) distribution in the brain but with variable intensities, which could be explained by different stages in the progression of the disease. We propose that the BPDC could be used as a tool to differentiate classical cases of BSE from the recently identified atypical BSE cases.

Analysis of the risk of transmitting bovine spongiform encephalopathy through bone grafts derived from bovine bone

Bone substitutes of bovine origin are widely used for treatment of bone defects in dental and orthopedic surgery. Due to the occurrence of BSE and the new variant of Creutzfeldt Jakob Disease risks of transmitting diseases through the use of such materials need to be carefully evaluated. Risk analysis can either be based on theoretical assessments or experimental evidence. Here we present a comparative study on two bovine bone substitutes (Bio-Oss and Osteograf/N) which is based on theoretical values. Furthermore, for one of these materials, i.e. Bio-Oss, the prion inactivation capacity of one of the production steps was experimentally evaluated. Theoretical and experimental data indicate that the use of these materials does not carry a risk of transmitting BSE to patients.

Prevention of scrapie pathogenesis by transgenic expression of anti-prion protein antibodies

Variant Creutzfeldt-Jakob disease and bovine spongiform encephalopathy are initiated by extracerebral exposure to prions. Although prion transmission from extracerebral sites to the brain represents a potential target for prophylaxis, attempts at vaccination have been limited by the poor immunogenicity of prion proteins. To circumvent this, we expressed an anti-prion protein (anti-PrP) mu chain in Prnp(o/o) mice. Transgenic mice developed sustained anti-PrP titers, which were not suppressed by introduction of Prnp+ alleles. Transgene expression prevented pathogenesis of prions introduced by intraperitoneal injection in the spleen and brain. Expression of endogenous PrP (PrP(C)) in the spleen and brain was unaffected, suggesting that immunity was responsible for protection. This indicates the feasibility of immunological inhibition of prion disease in vivo.

Application of Prionics Western blotting procedure to screen for BSE in cattle regularly slaughtered at Swiss abattoirs

Disease-specific PrP (PrP(Sc)) is at least part of the infectious particle (prion) causing bovine spongiform encephalopathy (BSE) or scrapie in sheep. Digestion with protease allows a distinction between normal PrP (PrP(C)) and PrP(Sc) i.e. PrP(C) is completely digested while PrP(Sc) is cleaved at the N-terminus leading to a fragment of reduced molecular weight (PrP 27-30). Detection of this fragment by Western blotting has been described more than a decade ago for rodent PrP. We have now optimized the technique in order to allow rapid analysis of hundreds of samples per day. Here we report the application of this technique to the analysis of 3000 regularly slaughtered cattle from Swiss abattoirs. For comparison all the animals were subsequently examined by classical methods (i.e. histology and immunohistochemistry). All but one animal were negative for BSE by all methods. The Western blot positive animal was confirmed to be a BSE case and the carcass was removed from the food chain. We conclude that it is feasible to examine slaughtered cattle on a routine basis without causing delays to the meat processing industry.

A monomer-dimer equilibrium of a cellular prion protein (PrPC) not observed with recombinant PrP

Both the purified normal (protease-sensitive) isoform of the prion protein (PrP(C)) (Pergami, P., Jaffe, H., and Safar, J. (1996) Anal. Biochem. 236, 63-73) and recombinant prion protein (PrP) have been found to be in monomeric form (Mehlhorn, I., Groth, D., Stockel, J., Moffat, B., Reilly, D., Yansura, D., Willet, W. S., Baldwin, M., Fletterick, R., Cohen, F. E., Vandlen, R., Henner, D., and Prusiner, S. B. (1996) Biochemistry 35, 5528-5537; and this paper), and therefore PrP(C)-PrP(C) interactions were previously unknown. In this report we confirm recombinant PrP to be a monomer by analytical ultracentrifugation. However, by three lines of evidence (enzyme-linked immunosorbent assay (ELISA), cross-linking experiments, and size exclusion chromatography) we could also demonstrate that, under native conditions, at least part of the native bovine PrP(C) exists as a monomer-dimer equilibrium. A bovine PrP(C)-specific immuno-sandwich ELISA was developed and calibrated with recombinant PrP (Meyer, R. K., Oesch, B., Fatzer, R., Zurbriggen, A., and Vandevelde, M. (1999) J. Virol. 73, 9386-9392). By this ELISA we identified a distinct PrP(C) fraction and partially purified this protein. When serial dilutions of brain homogenate or partially purified PrP(C) were measured, using the peptide antibody C15S, a nonlinear dose-response curve was obtained. This nonlinearity was shown not to be due to an artifact of the procedure but to a monomer-dimer equilibrium of PrP(C) with preferential binding of the antibody to the dimer. From the curvature we could deduce the association constant (3.9 x 10(8) M(-1) at 37 degrees C). Accordingly, DeltaG degrees of the reaction was calculated (-48.6 kJ M(-1)), and DeltaH degrees (9.5 kJ M(-1)) as well as DeltaS degrees (0.2 kJ K(-1) M(-1)) were extrapolated from the van't Hoff plot. When serial dilutions of monomeric recombinant PrP were tested, only a straight line was obtained, supporting our hypothesis. Additional evidence of dimer formation was revealed by Western blotting of partially purified PrP(C) cross-linked by the homobifunctional cross-linker BS(3). Finally, size exclusion chromatography of partially purified PrP(C) fractions revealed an additional shoulder not observed with recombinant PrP. The difference in respect of dimer formation between native PrP(C) and recombinant PrP could be explained by the lack of glycosylation of the latter.

Detection of bovine spongiform encephalopathy-specific PrP(Sc) by treatment with heat and guanidine thiocyanate

The conversion of a ubiquitous cellular protein (PrP(C)), an isoform of the prion protein (PrP), to the pathology-associated isoform PrP(Sc) is one of the hallmarks of transmissible spongiform encephalopathies such as bovine spongiform encephalopathy (BSE). Accumulation of PrP(Sc) has been used to diagnose BSE. Here we describe a quantitative enzyme-linked immunosorbent assay (ELISA) that involves antibodies against epitopes within the protease-resistant core of the PrP molecule to measure the amount of PrP in brain tissues from animals with BSE and normal controls. In native tissue preparations, little difference was found between the two groups. However, following treatment of the tissue with heat and guanidine thiocyanate (Gh treatment), the ELISA discriminated BSE-specific PrP(Sc) from PrP(C) in bovine brain homogenates. PrP(Sc) was identified by Western blot, centrifugation, and protease digestion experiments. It was thought that folding or complexing of PrP(Sc) is most probably reversed by the Gh treatment, making hidden antigenic sites accessible. The digestion experiments also showed that protease-resistant PrP in BSE is more difficult to detect than that in hamster scrapie. While the concentration of PrP(C) in cattle is similar to that in hamsters, PrP(Sc) sparse in comparison. The detection of PrP(Sc) by a simple physicochemical treatment without the need for protease digestion, as described in this study, could be applied to develop a diagnostic assay to screen large numbers of samples.

Validation of a western immunoblotting procedure for bovine PrP(Sc) detection and its use as a rapid surveillance method for the diagnosis of bovine spongiform encephalopathy (BSE)

In this report we document the results of several independent studies testing the sensitivity, specificity and reliability of the Prionics Western blotting (PWB) procedure to detect bovine and ovine disease-specific, protease-resistant prion protein (PrP(Sc)). Validation of the technique was obtained by blind analysis of samples from cattle affected with bovine spongiform encephalopathy (BSE), clinically normal animals or cattle with neurological diseases unrelated to BSE. Overall, very high sensitivity, specificity and reliability was observed. It became clear that sampling of the correct brain region and the method used for protein extraction are important factors for correct diagnosis. Furthermore, we tested the usefulness of the PWB technique as an instrument for surveillance purposes. We analyzed animals from a culling scheme as well as older animals from abattoirs to determine the number of subclinical BSE cases detectable by histopathological examination, immunohistochemistry for PrP(Sc) and PWB. In both studies, BSE-affected animals with no overt clinical symptoms were detected. These results demonstrate the usefulness of the PWB procedure in surveillance systems serving as a rapid diagnostic tool to identify animals subclinically infected with BSE.

Monoclonal antibodies specific for the native, disease-associated isoform of the prion protein

Reviewing the circumstances that have led to the first monoclonal antibody against the disease-associated form of PrP, we consider the availability of PrP knockout mice and recombinant PrP, as well as a reliable conformational screening protocol as being important prerequisites for a successful immunization approach. When considering presenting an antigen to a mouse with the goal of obtaining specific monoclonal antibodies against a misfolded or aggregated form of a host protein, it is desirable to increase the definition of a subtle conformational difference. This can be achieved by immunizing an antigen knockout mouse that has not developed self-tolerance against the respective antigen. Furthermore, if conformational isoforms and/or oligomeric forms of a protein sequence are understood to exist in an equilibrium, high and pure amounts of recombinant protein may increase the likelihood that a particular population of protein conformation passes an antigenic threshold necessary to start an immunogenic response. Pulling out the monoclonal antibodies by correct screening is essential. Screening against the pure misfolded or aggregated protein is often complicated by its poor solubility and hence the ability to immobilize. In the present case, immobilization of disease-associated PrP on nitrocellulose had been established as a conformation-sensitive screening method, allowing to "freeze" PrP in its distinguishable, disease-associated conformation. We are cautious to generalize conclusions of how to assess the generation of monoclonal antibodies against these particular protein isoforms to other diseases of protein misfolding and/or aggregation, but ultimately the present approach may inspire respective experiments.

Prion (PrPSc)-specific epitope defined by a monoclonal antibody

Prions are infectious particles causing transmissible spongiform encephalopathies (TSEs). They consist, at least in part, of an isoform (PrPSc) of the ubiquitous cellular prion protein (PrPC). Conformational differences between PrPC and PrPSc are evident from increased beta-sheet content and protease resistance in PrPSc. Here we describe a monoclonal antibody, 15B3, that can discriminate between the normal and disease-specific forms of PrP. Such an antibody has been long sought as it should be invaluable for characterizing the infectious particle as well as for diagnosis of TSEs such as bovine spongiform encephalopathy (BSE) or Creutzfeldt-Jakob disease (CJD) in humans. 15B3 specifically precipitates bovine, murine or human PrPSc, but not PrPC, suggesting that it recognizes an epitope common to prions from different species. Using immobilized synthetic peptides, we mapped three polypeptide segments in PrP as the 15B3 epitope. In the NMR structure of recombinant mouse PrP, segments 2 and 3 of the 15B3 epitope are near neighbours in space, and segment 1 is located in a different part of the molecule. We discuss models for the PrPSc-specific epitope that ensure close spatial proximity of all three 15B3 segments, either by intermolecular contacts in oligomeric forms of the prion protein or by intramolecular rearrangement.

Recombinant full-length murine prion protein, mPrP(23-231): purification and spectroscopic characterization

The cellular prion protein of the mouse, mPrP(C), consists of 208 amino acids (residues 23-231). It contains a carboxy-terminal domain, mPrP(121-231), which represents an autonomous folding unit with three alpha-helices and a two-stranded antiparallel beta-sheet. We expressed the complete amino acid sequence of the prion protein, mPrP(23-231), in the cytoplasm of Escherichia coli. mPrP(23-231) was solubilized from inclusion bodies by 8 M urea, oxidatively refolded and purified to homogeneity by conventional chromatographic techniques. Comparison of near-UV circular dichroism, fluorescence and one-dimensional 1H-NMR spectra of mPrP(23-231) and mPrP(121-231) shows that the amino-terminal segment 23-120, which includes the five characteristic octapeptide repeats, does not contribute measurably to the manifestation of three-dimensional structure as detected by these techniques, indicating that the residues 121-231 might be the only polypeptide segment of PrP(C) with a defined three-dimensional structure.

Altered circadian activity rhythms and sleep in mice devoid of prion protein

There is a wealth of data supporting a central role for the prion protein (PrP) in the neurodegenerative prion diseases of both humans and other species, yet the normal function of PrP, which is expressed at the cell surface of neurons and glial cells, is unknown. It has been speculated that neuropathology may be due to loss of normal function of PrP. Here we show that in mice devoid of PrP there is an alteration in both circadian activity rhythms and patterns. To our knowledge, this is the first null mutation that has been shown to affect sleep regulation and our results indicate that at least one of the inherited prion diseases, fatal familial insomnia, where there is a profound alteration in sleep and the daily rhythms of many hormones, may be related to the normal function of the prion protein.

Prion protein (PrP) with amino-proximal deletions restoring susceptibility of PrP knockout mice to scrapie

The 'protein only' hypothesis postulates that the prion, the agent causing transmissible spongiform encephalopathies, is PrP(Sc), an isoform of the host protein PrP(C). Protease treatment of prion preparations cleaves off approximately 60 N-terminal residues of PrP(Sc) but does not abrogate infectivity. Disruption of the PrP gene in the mouse abolishes susceptibility to scrapie and prion replication. We have introduced into PrP knockout mice transgenes encoding wild-type PrP or PrP lacking 26 or 49 amino-proximal amino acids which are protease susceptible in PrP(Sc). Inoculation with prions led to fatal disease, prion propagation and accumulation of PrP(Sc) in mice expressing both wild-type and truncated PrPs. Within the framework of the 'protein only' hypothesis, this means that the amino-proximal segment of PrP(C) is not required either for its susceptibility to conversion into the pathogenic, infectious form of PrP or for the generation of PrP(Sc).

Developmental expression of the prion protein gene in glial cells

Replication of prions is dependent on the presence of the host protein PrPc. During the course of disease, PrPc is converted into an abnormal isoform, PrPSc, which accumulates in the brain. Attempts to identify the cell type(s) in which prion replication and PrP conversion occur have reached conflicting results. Although PrP mRNA is present in high amounts in neurons throughout the life of the animal, PrPSc initially accumulates in astrocytes and possibly other glial cells and, later in the course of the disease, spreads diffusely in the tissue, often in white matter. We report here that PrP mRNA is expressed not only in neurons but also in astrocytes and oligodendrocytes throughout the brain of postnatal hamsters and rats. The level of glial Prp mRNA expression in neonatal animals was comparable to that of neurons and increased two-fold during postnatal development. A substantial portion of brain PrP mRNA is therefore contributed by glial cells. Our results provide an explanation for the accumulation of PrPSc in white matter tissue and in the cytoplasm of glial cells and argue for a direct involvement of glia in prion propagation.

Properties of the scrapie prion protein: quantitative analysis of protease resistance

The disease-specific isoform of the prion protein (PrPSc) is an essential part of the infectious particle which causes spongiform degeneration in various mammalian species. PrPSc differs from PrP of normal animals (PrPc) by its relative protease resistance. The physical nature of this difference is still unknown. We analyzed the protease resistance of PrPSc quantitatively using an enzyme-linked immunofiltration assay. PrPSc was rendered completely protease-sensitive at alkaline pH or in > 1.5 M guanidinium thiocyanate (GdnSCN). Denaturation in 4 M GdnSCN completely abolished the protease resistance of PrPSc within 15 min, while denaturation in 7.2 M urea showed a slower time course. In the presence of ethanol, PrPSc was protected from denaturation by GdnSCN or alkaline pH. Denaturation curves were used to calculate the free energy (delta GD) as a function of different denaturant concentrations. Linear regression of delta GD values was used to extrapolate the free energy in the absence of denaturants (delta GH2O), yielding similar values (delta GH2O,GdnSCN = -2.3 kcal/mol; delta GH2O,urea = -3.1 kcal/mol). The linear relationship between delta GD and the denaturant concentration is suggestive of a two-state model involving the conformational change of a single protein domain. This is also reflected in the small number of side chains (11.6) additionally exposed to the solvent upon conversion of PrPSc to its protease-sensitive isoform. Our results suggest that only minor rearrangements of the structure of PrP are needed to abolish the protease resistance of PrPSc.

Characterization of PrP binding proteins

Prions cause spongiform degeneration in various mammalian species. The scrapie prion protein (PrPSc) is part of the infectious particle and may mediate infection and spreading of the disease in the brain. It was therefore of interest to purify and analyse PrP ligands (Plis). Plis were identified on ligand blots using either intact PrP or peptides corresponding to the central portion of PrP. Here, characterization of a 110 and a 125 kDa Pli is reported. Both Plis were found in total membrane fractions and could be extracted with carbonate indicating that they are not integral membrane proteins. On sucrose gradients both PrP ligands sedimented with high density particles.

Normal development of nerve-muscle synapses in mice lacking the prion protein gene

The expression of acetylcholine receptors (AChR) at neuromuscular synapses in skeletal muscle is regulated by innervation. Recent evidence suggests that the neurotrophic factors involved in the expression of AChR subunit genes may be related to the prion protein (PrPc), a protein of unknown function expressed primarily in neurons which, in its modified form, PrPSc, is thought to have a role in the pathogenesis of transmissible spongiform encephalopathies. We have tested for an involvement of PrPc in the neurotrophic regulation of synaptic AChRs in muscle by comparing the contents of AChR epsilon- and gamma-subunit mRNAs by Northern blot analysis and by in situ hybridization in mice with normal and with deleted PrP genes. At the protein level, AChR expression was assessed electrophysiologically. No difference was found between muscles from the two types of animals, suggesting that the neural regulation of AChR subunit expression in skeletal muscle can be mediated by factors that are not derived from the PrP gene.

Molecular cloning of a candidate chicken prion protein

Fractions enriched for acetylcholine receptor-inducing activity from chicken brain were found to contain a protein that was approximately 30% homologous with mammalian prion proteins [Harris, D. A., Falls, D. L., Johnson, F. A. & Fischbach, G. D. (1991) Proc. Natl. Acad. Sci. USA 88, 7664-7668]. To extend these observations, we recovered genomic clones encoding a putative chicken prion protein (PrP). Like mammalian PrP molecules, the candidate chicken PrP is encoded by a single-copy gene and the entire open reading frame is found within a single exon. All of the structural features of mammalian PrP were found in the chicken protein. When the N-terminal repeats of PrP were not considered, the chicken and mammalian proteins were approximately 55% homologous, allowing for conservative substitutions. Screening of a chicken genomic DNA library failed to identify a more closely related chicken PrP homologue. These findings argue that the protein which purifies with acetylcholine receptor-inducing activity is chicken PrP.

Genetics of prion infections

Although the infectious prions causing scrapie and several human transmissible neurodegenerative diseases resemble viruses in many respects, molecular and genetic analyses indicate that prions are fundamentally different from viruses in their structure and the mechanisms by which they cause disease. The only macromolecule that has been identified in infectious prion preparations is a disease-specific isoform of the prion protein, which is encoded by a host gene. A growing body of data supports the contention that prion infections represent a novel host-pathogen interaction.

Identification of cellular proteins binding to the scrapie prion protein

The scrapie prion protein (PrPSc) is an abnormal isoform of the cellular protein PrPc. PrPSc is found only in animals with scrapie or other prion diseases. The invariable association of PrPSc with infectivity suggests that PrPSc is a component of the infectious particle. In this study, we report the identification of two proteins from hamster brain of 45 and 110 kDa (denoted PrP ligands Pli 45 and Pli 110) which were able to bind to PrP 27-30, the protease-resistant core of PrPSc on ligand blots. Pli 45 and Pli 110 also bound PrPC. Both Pli's had isoelectric points of approximately 5. The dissociation rate constant of the Pli 45/PrP 27-30 complex was 3 x 10(-6) s-1. Amino acid and protein sequence analyses were performed on purified Pli 45. Both the composition and the sequence were almost identical with those predicted for mouse glial fibrillary acidic protein (GFAP). Furthermore, antibodies to Pli 45 reacted with recombinant GFAP. The identification of proteins which interact with the PrP isoforms in normal and diseased brain may provide new insights into the function of PrPC and into the molecular mechanisms underlying prion diseases.

Scrapie and cellular PrP isoforms are encoded by the same chromosomal gene

PrP 27-30 is the major protein in purified preparations of scrapie agent. An almost complete PrP cDNA was used to select PrP-related genomic clones from normal hamster DNA. The gene contains a noncoding exon of 56 to 82 bp and a 2 kb coding exon, separated by a 10 kb intron. Transcription initiates at the same multiple sites in vivo and in vitro. The promoter lacks a TATA box and contains three repeats of the sequence GCCCCGCCC, which resembles the Sp1 binding site found in "housekeeping" genes. The PrP coding sequence encodes a presumptive amino-terminal signal peptide. The primary structure of PrP encoded by the gene of a healthy animal does not differ from that encoded by a cDNA from a scrapie-infected animal, suggesting that the different properties of PrP from normal and scrapie-infected brains are due to post-translational events.

A cellular gene encodes scrapie PrP 27-30 protein

A clone encoding PrP 27-30, the major protein in purified preparations of scrapie agent, was selected from a scrapie-infected hamster brain cDNA library by oligonucleotide probes corresponding to the N terminus of the protein. Southern blotting with PrP cDNA revealed a single gene with the same restriction patterns in normal and scrapie-infected brain DNA. A single PrP-related gene was also detected in murine and human DNA. PrP-related mRNA was found at similar levels in normal and scrapie-infected hamster brain, as well as in many other normal tissues. Using antisera against PrP 27-30, a PrP-related protein was detected in crude extracts of infected brain and to a lesser extent in extracts of normal brain. Proteinase K digestion yielded PrP 27-30 in infected brain extract, but completely degraded the PrP-related protein in normal brain extract. No PrP-related nucleic acids were found in purified preparations of scrapie prions, indicating that PrP 27-30 is not encoded by a nucleic acid carried within the infectious particles.

X-ray absorption near edge structure (XANES) determination of calcium sites of troponin C and parvalbumin

Using synchrotron radiation at the Frascati storage ring ADONE, the X-ray Absorption Near Edge Structure (XANES) has been applied to determine homologies and modifications of the local structure of the calcium binding sites of troponin C. In all four calcium binding sites, Ca2+ appears to be co-ordinated to carboxyl and carbonyl groups in a characteristic configuration. No structural difference has been found between high and low-affinity sites. A distortion of the Ca2+ site geometry by binding of Mg2+ has been observed. The XANES of parvalbumin has been measured and found to be different from troponin C. A tentative identification of the characteristic XANES spectra of the two different Ca2+ sites in this protein is reported.

New surface component of fibroblast's focal contacts identified by a monoclonal antibody

We describe a monoclonal antibody (anti-FC-1) that inhibits the attachment of chicken embryo fibroblasts to artificial substrates. In the immunofluorescence, anti-FC-1 also stained the focal contacts of the fibroblasts, organelles suggested to be involved in cell-substrate adhesion. This antibody was absorbed on the surface of intact fibroblasts, and its action was blocked by cell extracts with nonionic detergents, indicating that the antigen (FC-1) is a surface membrane protein. Triton-extracted FC-1 exhibited a molecular weight of approximately 500,000, and a 60,000 dalton protein was immunoprecipitated from 35S-methionine-labeled cells. We have thus characterized a new protein at the exterior side of fibroblast's focal contacts. To determine to what degree this protein mediates the adhesion of the cells to the substrate, and whether it also interacts with the cytoskeletal elements on the cytoplasmic side, will require further investigation.

An example of enzyme hysteresis. The slow and tight interaction of some fully competitive inhibitors with small intestinal sucrase

Of the fully competitive inhibitors of small intestinal sucrase investigated in this or in other papers, acarbose, nojirimycin, and deoxynojirimycin (Fig. 2) have the highest affinity for the enzyme, their Ki values being in the 10(-7)-10(-8) M range. Furthermore, thier interaction with the enzyme is slow, the steady state being reached in their presence in a matter of minutes. Their overall "on" and "off" constants are small, which indicates that a conformational change accompanies the interaction of these substances with the active site of intestinal sucrase. The structure of these inhibitors, as well as the pH dependence of their Ki values, agrees with and allows additions to be made to the catalytic mechanism earlier suggested for this enzyme (Cogoli, A., and Semenza, G. (1975) J. Biol. Chem. 250, 7802-7809). None of these inhibitors of sucrase has any sizeable effect on the small intestinal Na+-dependent D-glucose transport system.