Prions: disease propagation and disease therapy by conformational transmission

Cofactors facilitate bona fide prion misfolding in vitro but are not necessary for the infectivity of recombinant murine prions

Prion diseases, particularly sporadic cases, pose a challenge due to their complex nature and heterogeneity. The underlying mechanism of the spontaneous conversion from PrPC to PrPSc, the hallmark of prion diseases, remains elusive. To shed light on this process and the involvement of cofactors, we have developed an in vitro system that faithfully mimics spontaneous prion misfolding using minimal components. By employing this PMSA methodology and introducing an isoleucine residue at position 108 in mouse PrP, we successfully generated recombinant murine prion strains with distinct biochemical and biological properties. Our study aimed to explore the influence of a polyanionic cofactor in modulating strain selection and infectivity in de novo-generated synthetic prions. These results not only validate PMSA as a robust method for generating diverse bona fide recombinant prions but also emphasize the significance of cofactors in shaping specific prion conformers capable of crossing species barriers. Interestingly, once these conformers are established, our findings suggest that cofactors are not necessary for their infectivity. This research provides valuable insights into the propagation and maintenance of the pathobiological features of cross-species transmissible recombinant murine prion and highlights the intricate interplay between cofactors and prion strain characteristics.

Impact of flexibility on the aggregation of polymeric macromolecules

Dependence of the dimerization probability and the aggregation behavior of polymeric macromolecules on their flexibility is studied using Langevin dynamics simulations. It is found that the dimerization probability is a non-monotonic function of the polymers persistence length. For a given value of inter-polymer attraction strength, semiflexible polymers have lower dimerization probability relative to flexible and rigid polymers of the same length. The threshold temperature of the formation of aggregates in a many-polymer system and its dependence on the polymers persistence length is also investigated. The simulation results of two- and many-polymer systems are in good agreement and show how the amount of flexibility affects the dimerization and the aggregation behaviors of polymeric macromolecules.

Realization of Amyloid-like Aggregation as a Common Cause for Pathogenesis in Diseases

Amyloids were conventionally referred to as extracellular and intracellular accumulation of Aβ42 peptide, which causes the formation of plaques and neurofibrillary tangles inside the brain leading to the pathogenesis in Alzheimer's disease. Subsequently, amyloid-like deposition was found in the etiology of prion diseases, Parkinson's disease, type II diabetes, and cancer, which was attributed to the aggregation of prion protein, α-Synuclein, islet amyloid polypeptide protein, and p53 protein, respectively. Hence, traditionally amyloids were considered aggregates formed exclusively by proteins or peptides. However, since the last decade, it has been discovered that other metabolites, like single amino acids, nucleobases, lipids, glucose derivatives, etc., have a propensity to form amyloid-like toxic assemblies. Several studies suggest direct implications of these metabolite assemblies in the patho-physiology of various inborn errors of metabolisms like phenylketonuria, tyrosinemia, cystinuria, and Gaucher's disease, to name a few. In this review, we present a comprehensive literature overview that suggests amyloid-like structure formation as a common phenomenon for disease progression and pathogenesis in multiple syndromes. The review is devoted to providing readers with a broad knowledge of the structure, mode of formation, propagation, and transmission of different extracellular amyloids and their implications in the pathogenesis of diseases. We strongly believe a review on this topic is urgently required to create awareness about the understanding of the fundamental molecular mechanism behind the origin of diseases from an amyloid perspective and possibly look for a common therapeutic strategy for the treatment of these maladies by designing generic amyloid inhibitors.

scFv-oligopeptide chaperoning system-assisted on-column refolding and purification of human muscle creatine kinase from inclusion bodies

The formation of inclusion bodies in bacterial hosts poses a major challenge for the large-scale recovery of bioactive proteins. The process of obtaining bioactive protein from inclusion bodies is labor intensive, and the yields of recombinant protein are often low. Here, we describe a novel method for the renaturation and purification of inclusion bodies. This method combines a scFv-oligopeptide chaperoning system and an on-column refolding system to help refold human muscle creatine kinase (HCK) inclusion bodies. This method could significantly increase the activity recovery of denatured HCK inclusion bodies and provides an effective method for the production of bioactive proteins from inclusion bodies.

Fluorescent Diagnostic Probes in Neurodegenerative Diseases

Neurodegenerative diseases are debilitating disorders that feature progressive and selective loss of function or structure of anatomically or physiologically associated neuronal systems. Both chronic and acute neurodegenerative diseases are associated with high morbidity and mortality along with the death of neurons in different areas of the brain; moreover, there are few or no effective curative therapy options for treating these disorders. There is an urgent need to diagnose neurodegenerative disease as early as possible, and to distinguish between different disorders with overlapping symptoms that will help to decide the best clinical treatment. Recently, in neurodegenerative disease research, fluorescent-probe-mediated biomarker visualization techniques have been gaining increasing attention for the early diagnosis of neurodegenerative diseases. A survey of fluorescent probes for sensing and imaging biomarkers of neurodegenerative diseases is provided. These imaging probes are categorized based on the different potential biomarkers of various neurodegenerative diseases, and their advantages and disadvantages are discussed. Guides to develop new sensing strategies, recognition mechanisms, as well as the ideal features to further improve neurodegenerative disease fluorescence imaging are also explored.

Prion protein amplification techniques

Protein amplification techniques exploit the ability of PrP^TSE to induce a conformational change in prion protein (PrP) in a continuous fashion, so that the small amount of PrP^TSE found in tissues and biologic fluids in prion diseases can be amplified to a point where they are detectable by conventional laboratory techniques. The most widely used protein aggregation assays are protein misfolding cyclic amplification assay (PMCA) and real-time quaking-induced conversion (RT-QuIC). These assays have been used extensively in both animal and human prion disease in studies ranging from the development of diagnostics, understanding disease transmission potential, to investigating mechanisms underlying neurodegeneration. In human prion disease, cerebrospinal fluid (CSF) RT-QuIC analysis has been shown to be a highly sensitive and specific test for sporadic Creutzfeldt-Jakob disease (sCJD) and has now been included in the diagnostic criteria. It is also a useful investigation for some genetic forms of prion disease where other cerebrospinal fluid tests may be negative. PMCA shows great potential for the diagnosis of variant CJD (vCJD) and has the ability to distinguish vCJD from sCJD, which may become increasingly important with emergence of a patient with neuropathologically confirmed vCJD associated with PRNP codon129MV, which indicates that a new wave of vCJD cases is likely and that these may be difficult to distinguish from sCJD.

Protein Misfolding Cyclic Amplification of Infectious Prions

Transmissible spongiform encephalopathies, or prion diseases, are a group of incurable disorders caused by the accumulation of an abnormally folded prion protein (PrP^Sc) in the brain. According to the "protein-only" hypothesis, PrP^Sc is the infectious agent able to propagate the disease by acting as a template for the conversion of the correctly folded prion protein (PrP^C) into the pathological isoform. Recently, the mechanism of PrP^C conversion has been mimicked in vitro using an innovative technique named protein misfolding cyclic amplification (PMCA). This technology represents a great tool for studying diverse aspects of prion biology in the field of basic research and diagnosis. Moreover, PMCA can be expanded for the study of the misfolding process associated to other neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and frontotemporal lobar degeneration.

The Endoplasmic Reticulum Chaperone GRP78/BiP Modulates Prion Propagation in vitro and in vivo

Prion diseases are fatal neurodegenerative disorders affecting several mammalian species, characterized by the accumulation of the misfolded form of the prion protein, which is followed by the induction of endoplasmic reticulum (ER) stress and the activation of the unfolded protein response (UPR). GRP78, also called BiP, is a master regulator of the UPR, reducing ER stress levels and apoptosis due to an enhancement of the cellular folding capacity. Here, we studied the role of GRP78 in prion diseases using several in vivo and in vitro approaches. Our results show that a reduction in the expression of this molecular chaperone accelerates prion pathogenesis in vivo. In addition, we observed that prion replication in cell culture was inversely related to the levels of expression of GRP78 and that both proteins interact in the cellular context. Finally, incubation of PrP^Sc with recombinant GRP78 led to the dose-dependent reduction of protease-resistant PrP^Scin vitro. Our results uncover a novel role of GRP78 in reducing prion pathogenesis, suggesting that modulating its levels/activity may offer a novel opportunity for designing therapeutic approaches for these diseases. These findings may also have implications for other diseases involving the accumulation of misfolded proteins.

Rapid size-dependent separation of CdTe quantum dots with prion protein

rPrP can be applied to separate quantum dots with different size.

pH-dependent self-assembly of EAK16 peptides in the presence of a hydrophobic surface: coarse-grained molecular dynamics simulation

Self-assembly behavior of the three types of ionic peptide, EAK16, is studied in the presence of a hydrophobic surface using coarse-grained molecular dynamics simulations at three pH ranges of the solution. It is found that the peptide chains of all the three types assemble on the hydrophobic surface. EAK16-I and EAK16-II peptides assemble into ribbon-like structures, regardless of the value of pH. EAK16-IV peptide chains, however, assemble into ribbon-like structures at low and high pH ranges and form disc-shaped assemblies on the hydrophobic surface at the isoelectric point, pH = 7. Strong intra-chain electrostatic interactions in the case of EAK16-IV peptide play the main role in dependence of its self-assembly behavior on pH and the different morphology of its assembly relative to those of the two other types. Kinetics of growth of the assemblies on the hydrophobic surface is also studied.

The extent of protease resistance of misfolded prion protein is highly dependent on the salt concentration

Transmissible spongiform encephalopathies are neurodegenerative diseases caused by prions in mammals. An aberrantly folded protein (PrP(Sc)) is the main component of these proteinaceous infectious particles. Prions exhibit strong resistance to protease digestion, which is typically exploited for biochemical discrimination from its native cellular form (PrP(C)). This classical feature has been partially challenged by the isolation of sizeable amounts of protease-sensitive PrP(Sc) isoforms that self-propagate in vivo. Here, we report that the degree of PrP(Sc) protease resistance is highly dependent on the concentration of salt in the solution. Similar changes were observed in PrP(Sc) obtained from different strains and species. Strikingly, the effect of salt is reversible and is associated with changes on the size of PrP(Sc) particles, but surprisingly, the more protease-sensitive species consists of a larger size. These findings shed light on the mechanistic aspects of prion proteolysis and should be considered when assessing samples of biomedical relevance.

Cyclic amplification of prion protein misfolding

Protein misfolding cyclic amplification (PMCA) is a technique that takes advantage of the nucleation-dependent prion replication process to accelerate the conversion of PrP(C) into PrP(Sc) in the test tube. PMCA uses ultrasound waves to fragment the PrP(Sc) polymers, increasing the amount of seeds present in the infected sample without affecting their ability to act as conversion nuclei. Over the past 5 years, PMCA has become an invaluable technique to study diverse aspects of prions. The PMCA technology has been used by several groups to understand the molecular mechanism of prion replication, the cellular factors involved in prion propagation, the intriguing phenomena of prion strains and species barriers, to detect PrP(Sc) in tissues and biological fluids, and to screen for inhibitors against prion replication. In this chapter, we describe a detailed protocol of the PMCA technique, highlighting some of the important technical aspects to obtain a successful and reproducible application of the technology.

THE SPREAD OF PRION DISEASES IN THE BRAIN — MODELS OF REACTION AND TRANSPORT ON NETWORKS

In this paper we will present a modeling approach to describe the progression and the spread of prion diseases in the brain. Although there exist a number of mathematical models for the interaction of prions with their native counterpart, prion transport and spread is usually neglected. The concentration dynamics of prions, and thus the dynamics of the disease progression, however, are influenced by prion transport, especially in a medium as complex as the brain. Therefore, we focus here on the interaction between prion concentration dynamics and prion transport. The model is constructed by combining a model of prion-prion interaction with transport on networks. The approach leads to a system of reaction-diffusion equations, whereby the diffusion term is discrete. The equations are solved numerically on domains given as large networks. We show that the prion concentration grows faster on networks characterized by a higher degree heterogeneity. Furthermore, we introduce cell death as a consequence of increasing prion concentration, leading to network decomposition. We show that infectious diseases destroy networks similarly to targeted attacks, namely by affecting the nodes with the highest degree first. Relating the incubation period and disease progression to the process of network decomposition, we find that, interestingly, a long incubation time followed by sudden onset and fast progression of the disease does not need to be reflected in the overall concentration dynamics of the infective agent.

Prion protein misfolding affects calcium homeostasis and sensitizes cells to endoplasmic reticulum stress

Prion-related disorders (PrDs) are fatal neurodegenerative disorders characterized by progressive neuronal impairment as well as the accumulation of an abnormally folded and protease resistant form of the cellular prion protein, termed PrP^RES. Altered endoplasmic reticulum (ER) homeostasis is associated with the occurrence of neurodegeneration in sporadic, infectious and familial forms of PrDs. The ER operates as a major intracellular calcium store, playing a crucial role in pathological events related to neuronal dysfunction and death. Here we investigated the possible impact of PrP misfolding on ER calcium homeostasis in infectious and familial models of PrDs. Neuro2A cells chronically infected with scrapie prions showed decreased ER-calcium content that correlated with a stronger upregulation of UPR-inducible chaperones, and a higher sensitivity to ER stress-induced cell death. Overexpression of the calcium pump SERCA stimulated calcium release and increased the neurotoxicity observed after exposure of cells to brain-derived infectious PrP^RES. Furthermore, expression of PrP mutants that cause hereditary Creutzfeldt-Jakob disease or fatal familial insomnia led to accumulation of PrP^RES and their partial retention at the ER, associated with a drastic decrease of ER calcium content and higher susceptibility to ER stress. Finally, similar results were observed when a transmembrane form of PrP was expressed, which is proposed as a neurotoxic intermediate. Our results suggest that alterations in calcium homeostasis and increased susceptibility to ER stress are common pathological features of both infectious and familial PrD models.

The role of lipid–protein interactions in amyloid-type protein fibril formation

Structural transition of polypeptide chains into the beta-sheet state followed by amyloid fibril formation is the key characteristic of a number of the so-called conformational diseases. The multistep process of protein fibrillization can be modulated by a variety of factors, in particular by lipid-protein interactions. A wealth of experimental evidence provides support to the notion that amyloid fibril assembly and the toxicity of pre-fibrillar aggregates are closely related and are both intimately membrane associated phenomena. The present review summarizes the principal factors responsible for the enhancement of fibril formation in a membrane environment, viz. (i) structural transformation of polypeptide chain into a partially folded conformation, (ii) increase of the local concentration of a protein upon its membrane binding, (iii) aggregation-favoring orientation of the bound protein, and (iv) variation in the depth of bilayer penetration affecting the nucleation propensity of the membrane associated protein. The molecular mechanisms of membrane-mediated protein fibrillization are discussed. Importantly, the toxicity of lipid-induced pre-fibrillar aggregates is likely to have presented a very strong negative selection pressure in the evolution of amino acid sequences.

Prion diseases: current understanding of epidemiology and pathogenesis, and therapeutic advances

The bovine spongiform encephalopathy (BSE) epidemic, along with the related threat to human health posed by the transmission of the BSE agent to humans, has highlighted the importance of prion diseases. These fatal neurodegenerative diseases are characterised by spongiform changes in the CNS, and comprise a wide spectrum of clinicopathological entities in humans and animals, such as Creutzfeldt-Jakob disease (CJD) and its emerging new variant (vCJD) in humans, and BSE and scrapie in animals. This article reviews the geographical distribution and the temporal trends of CJD and vCJD; the major events in the pathogenesis of prion diseases; the risk factors for sporadic CJD and vCJD; and the possible strategies for treating them. Worldwide statistics indicate that sporadic CJD has a stable incidence of one case per million people per year; in contrast, the incidence of vCJD appears to have increased exponentially from its characterisation in 1994 to a peak in 2000. As of December 2005, 183 definite or probable cases of vCJD had been reported worldwide. The crucial event in the pathogenesis of prion diseases is the conversion of the normally occurring cellular prion protein (PrP(c)) into a pathogenic form, called protease-resistant PrP (PrP(res)) or scrapie PrP (PrP(sc)). Pathogenetic studies in rodent models have shown that PrP(sc) is found in the enteric nervous system and in the gut-associated lymphoid tissue following oral scrapie ingestion. The role of the lymphoreticular system in the pathogenesis of TSE seems to be related to the strains of agents and the host genotype. Therapeutic approaches to vCJD are mainly based on the inhibition or prevention of the pathological change that creates PrP(sc). Derivatives of acridine (such as mepacrine [quinacrine]) and the phenothiazine psychotropics have been proposed as possible therapies because of their activity in cellular models; however, neither class was able to affect the protease resistance of preexisting PrP fibrils. More encouragingly, in animal models of prion disease, tetracyclines were found to reduce prion infectivity by direct inactivation of PrP(sc). While these findings are promising, the suitability of these compounds for clinical use is still limited by their low efficacy once symptoms are apparent. Treatments based on the vaccination approach have also produced positive results, but further investigations are necessary to establish their clinical application.

A conformation- and avidity-based proofreading mechanism for the TCR–CD3 complex

During antigen recognition, T cells show high sensitivity and specificity, and a wide dynamic range. Paradoxically, these characteristics are based on low-affinity receptor-ligand interactions [between the T-cell antigen receptor (TCR-CD3) complex and the antigen peptide bound to MHC]. Recent evidence indicates that the TCR-CD3 is expressed as multivalent complexes in the membrane of non-stimulated T cells and that conformational changes in the TCR-CD3 can be induced by strong but not weak agonists. Here, we propose a thermodynamic model whereby the specificity of the TCR-CD3-pMHC interaction is explained by its multivalent nature. We also propose that the free energy barriers involved in the change in conformation of the receptor impose a response threshold and determine the kinetic properties of recognition. Finally, we suggest that multivalent TCR-CD3s can amplify signals by spreading them from pMHC-engaged TCR-CD3s to unengaged complexes as a consequence of the cooperativity in the system.

Amyloids, prions and the inherent infectious nature of misfolded protein aggregates

Misfolded aggregates present in amyloid fibrils are associated with various diseases known as "protein misfolding" disorders. Among them, prion diseases are unique in that the pathology can be transmitted by an infectious process involving an unprecedented agent known as a "prion". Prions are infectious proteins that can transmit biological information by propagating protein misfolding and aggregation. The molecular mechanism of prion conversion has a striking resemblance to the process of amyloid formation, suggesting that misfolded aggregates have an inherent ability to be transmissible. Intriguing recent data suggest that other protein misfolding disorders might also be transmitted by a prion-like infectious process.

Protein misfolding cyclic amplification for diagnosis and prion propagation studies

Diverse human disorders are thought to arise from the misfolding and aggregation of an underlying protein. Among them, prion diseases are some of the most intriguing disorders that can be transmitted by an unprecedented infectious agent, termed prion, composed mainly (if not exclusively) of the misfolded prion protein. The hallmark event in the disease is the conversion of the native prion protein into the disease-associated misfolded protein. We have recently described a novel technology to mimic the prion conversion process in vitro. This procedure, named protein misfolding cyclic amplification (PMCA), conceptually analogous to DNA amplification by polymerase chain reaction (PCR), has important applications for research and diagnosis. In this chapter we describe the rational behind PMCA and some of the many potential applications of this novel technology. We also describe in detail the technical and methodological aspects of PMCA, as well as its application in automatic and serial modes that have been developed with a view to improving disease diagnosis.

Effect of transition metals (Mn, Cu, Fe) and deoxycholic acid (DA) on the conversion of PrPCto PrPres

The PMCA (protein misfolding cyclic amplification) technique has been shown to drive the amplification of misfolded prion protein by PrP(Sc) seeds during several cycles of incubation-sonication. Here, we report that cyclic amplification of normal hamster brain homogenates treated with a number of transition metals (manganese [Mn], copper [Cu], and iron [Fe]) leads to conversion of PrP(C) into protease-resistant PrP(res). The efficiency of PrP(res) formation and the glycoforms induced by Mn were different from those obtained by Cu and Fe. Previous results have shown higher Mn and lower Cu levels in the affinity-purified PrP(Sc) from the brain of prion diseases compared with normal hamster brain homogenates. We focused on Mn because we observed higher levels of Mn in whole brain, mitochondria, and scrapie-associated fibril-enriched fractions from the brains of animals with prion disease. In the presence of minute quantities of Mn-induced PrP(res) template with a large amount of PrP(C), PrP(res) amplification is observed. A metal chelater, EDTA reverses the effect of Mn on PrP(res) amplification, suggesting that Mn may play a role in the formation of PrP(res). It has been proposed that metal-catalyzed oxidation of PrP leads to the oxidation of amino acids and extensive aggregation of oxidized PrP. Carboxyl acids such as deoxycholic acid (DA) are oxidized molecules produced by 3' oxidation pathway. In in vitro studies, the potent effect of Mn on PrP(res) amplification is augmented by DA in a dose-dependent manner. On the basis of the evidence of the elevated Mn levels in scrapie-associated fibril (SAF)-enriched preparations from the brains of animals with prion disease, Mn-loaded PrP and oxidized molecules such as carboxyl acids may contribute to the formation of the scrapie isoform of PrP in prion diseases.

Changing paradigms in dermatology: proteomics: a new approach to skin disease

Completion of the human genome sequence in 2001 heralded a new age in the understanding of cellular function. By eliminating the need for meticulous nucleotide identification of suspect proteins, a short segment can be identified and, within seconds the remaining sequences culled. Now, investigations can be more specifically targeted at the proteins themselves. Unlike the one gene, one protein approach of years past, proteomics is the field of unraveling the vast network of protein interactions within living cells. Recently, certain dermatologic conditions, such as psoriasis and eczema, have been shown to be the result of immune deregulation. By better understanding the proteins responsible for immune system function, targeted disruptions can alter tissue responses. It is in this vein that proteomics attempts to understand cellular regulation for the eventual therapeutic modification of biologic behavior.

Cyclic amplification of protein misfolding: application to prion-related disorders and beyond

Diverse human disorders, including the majority of neurodegenerative diseases, are thought to arise from the misfolding and aggregation of protein. We have recently described a novel technology to amplify cyclically misfolded proteins in vitro. This procedure, named protein misfolding cyclic amplification (PMCA), is conceptually analogous to DNA amplification by PCR and has tremendous implications for research and diagnosis. The PMCA concept has been proved on the amplification of prions implicated in the pathogenesis of transmissible spongiform encephalopathies. In this article we describe the rational behind PMCA and some of the many potential applications of this novel technology.

Laminin affects polymerization, depolymerization and neurotoxicity of Abeta peptide

Amyloid deposition in Alzheimer fibrils forms neurotoxic senile plaques in a process that may be modulated by associated proteins. In this work we demonstrate the ability of laminin-1 and laminin-2 to inhibit fibril formation and toxicity on cultured rat hippocampal neurons. We confirm that the laminin-1-derived peptide YFQRYLI inhibits efficiently both fibril formation and neurotoxicity and show that the IKVAV peptide inhibits amyloid neurotoxicity despite its slight inhibition of fibril formation. On other hand, laminin-1 induces disaggregation of preformed fibrils in vitro, characterized as a progressive disassembly of fibrils into protofibrils and further clearance of these latter species, leading to a continual inhibition of amyloid neurotoxicity.

Amyloid-fibril formation. Proposed mechanisms and relevance to conformational disease

The phenomenon of the transformation of proteins into amyloid-fibrils is of interest, firstly, because it is closely connected to the so-called conformational diseases, many of which are hitherto incurable, and secondly, because it remains to be explained in physical terms (energetically and structurally). The process leads to fibrous aggregates in the form of extracellular amyloid plaques, neuro-fibrillary tangles and other intracytoplasmic or intranuclear inclusions. In this review, basic principles common to the field of amyloid fibril formation and conformational disease are underlined. Existing models for the mechanism need to be tested by experiment. The kinetic and energetic bases of the process are reviewed. The main controversial issue remains the coexistence of more than one protein conformation. The possible role of oligomeric intermediates, and of domain-swapping is also discussed. Mechanisms for cellular defence and novel therapies are considered.

Amyloid fibril formation by human stefin B in vitro: immunogold labelling and comparison to stefin A

The mechanism by which proteins form amyloid fibrils is of high interest to the scientific community as its understanding could resolve questions relevant to conformational diseases. The structural and energetic basis of the process is still largely unknown. The main controversial issue is the co-existence of several protein conformations. Three models for the mechanism of protein fibrillogenesis have been proposed which need to be tested by experiments. In this report, amyloid fibrils grown from human stefin B (type I cystatin) are described. This physiologically relevant protein readily forms fibrils in vitro, in contrast to the homologue--human stefin A--which forms fibrils under extreme conditions only. In order to specifically label stefin B fibrils in vitro, rabbit polyclonal antibody and mouse monoclonal antibody A6/2 against human stefin B were used for immunogold labelling. Samples were examined by transmission electron microscopy. Fibrils of stefin B were strongly labelled using polyclonal antibody and Protein A gold, whereas no positive reaction was observed with monoclonal antibody A6/2.

Protein aggregation

Protein aggregation occurs in vivo as a result of improper folding or misfolding. Diverse diseases arise from protein misfolding and are now grouped under the term "protein conformational diseases", including most of the neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, the prion encephalopathies and Huntington's disease, as well as cystic fibrosis, sickle cell anemia and other less common conditions. The hallmark event in these diseases is a change in the secondary and/or tertiary structure of a normal, functional protein, leading to the formation of protein aggregates with various supramolecular organizations. In most cases the aggregates are organized in structurally well-defined fibrils forming amyloid deposits. The crucial feature of the amyloidogenic proteins is their structural instability induced either by mutations, post-translational modifications, or local conditions, such as pH, temperature, and co-solutes. The conformational change may promote the disease either by gain of a toxic activity or by the lack of biological function of the natively folded protein. As different molecular mechanisms are involved in the formation of the various forms of protein aggregates, the laboratory diagnostic approach remains frequently elusive.