Category: Mad Cow Disease

A new treatment route for bovine spongiform encephalopathy (BSE) and its human form Creutzfeldt Jakob disease (CJD) could be a step closer based on new results from scientists at the University of Leeds. The team has found that a protein called Glypican-1 plays a key role in the development of BSE.

Details are published November 20 in the open-access journal PLoS Pathogens.

BSE, commonly known as mad cow disease, is known to be caused by an infectious and abnormal form of the prion protein that is present on cells within the nervous system. But scientists have been unclear as to what causes the abnormality to occur.

The new research from Leeds' Faculty of Biological Sciences provides part of the answer. The researchers have shown that the presence of Glypican-1 causes the numbers of abnormal prion proteins to rise. In experiments, when levels of Glypican-1 were reduced in infected cells, the levels of the abnormal prion reduced as well.

The discovery was a mixture of scientific detective work and luck, according to Professor of Biochemistry, Nigel Hooper.

"We were looking at how the normal prion protein functions in cells and spotted that it was interacting with something," he said. "Some lateral thinking and deduction led us to Glypican-1 and when we carried out the experiment, we found we were right."

The researchers suggest that Glypican-1 acts as a scaffold bringing the two forms of the prion protein together and that this contact causes normal prions to mutate into the infectious form. They are currently seeking further funding to investigate their hypothesis.

The findings have implications for the treatment of both BSE and the human form of the disease, CJD, according to Professor Hooper.

"Now that we know the identity of one of the key molecules in the disease process, we may in the future be able to design drugs that target this."

Although the scientists mainly conducted experiments using cells infected with prions, it is also possible that Glypican-1 is involved in other diseases of the nervous system.

"While initial experiments haven't shown any link with other neurodegenerative diseases like Alzheimer's, we're not yet completely ruling that out," said Professor Hooper.

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Journal Reference:

1. Taylor DR, Whitehouse IJ, Hooper NM. Glypican-1 Mediates Both Prion Protein Lipid Raft Association and Disease Isoform Formation. PLoS Pathogens, 2009; 5 (11): e1000666 DOI: 10.1371/journal.ppat.1000666

Specific cells within the immune system could help explain why younger people are more susceptible to variant Creutzfeldt-Jakob disease, scientists believe.

Patients diagnosed with variant CJD are, on average, 28 years old but it has been unclear why older people are not as affected by the disease. Variant CJD is a rare, degenerative, fatal brain disorder in humans, according to the U.S. Centers for Disease Control and Prevention.

Research at The Roslin Institute of the University of Edinburgh has identified specific cells within the immune system that attract corrupted proteins – known as prions – linked to variant CJD and encourage them to multiply and spread.

The study, published in the Journal of Immunology, looked at how these cells behaved in mice and found that the cells were impaired in older mice. As a result, they were unable to trap and replicate the prions and the mice did not develop clinical disease.

Neil Mabbott, of The Roslin Institute, said: "It has always been unclear why younger people were more susceptible to variant CJD and the assumption that they were more likely to eat cheap meat products is far too simplistic.

"Understanding what happens to these cells, which are important for the body's immune responses, could help us develop better ways of diagnosing variant CJD or even find ways of preventing prions from spreading to the brain. It could also help to create a vaccine."

Prions accumulate in lymphoid tissues – part of the body's immune system that include the spleen, lymph nodes and tonsils – before spreading to the central nervous system where they kill off brain cells and cause neurological disease.

Attempts to estimate the number of people carrying variant CJD have relied upon identifying the presence of prions in tonsil and appendix samples collected during routine operations.

The latest study, funded by the Biotechnology and Biological Sciences Research Council, suggests that even more people may be infected than previously thought as researchers also found prions present in brain tissue from older mice, which had not developed clinical disease.

Even when prions were present in the brains of older mice, however, they were not always found in lymphoid tissues, suggesting that the prediction of cases may be underestimated. It is thought the prions may have spread to the brain before they died off in the lymphoid tissues.

 A new study shows that nervous system integrity and axonal properties may play a key role in prion diseases. The findings, from researchers at the Rudolf Virchow Center and the Institute of Virology of the University of Würzburg, expand our understanding of the development of prion disease and suggest novel targets for therapeutic and diagnostic approaches in its early stages. 

Despite growing awareness of prion diseases, such as bovine spongiform encephalopathy (BSE) and the human variant, Creutzfeldt-Jakob disease, the molecular mechanisms responsible for their development are still not completely understood. These diseases are associated with neuropathological symptoms that include dementia, motor system defects and amnesia, although previous observations identified molecular hallmarks in the absence of these neuropathological symptoms, creating a paradox. The recent work of Vladimir Ermolayev and colleagues helps resolve this paradox, bringing new insights into the key factors triggering the onset of the clinical disease.

Impaired axonal transport is known to be involved in the development of neurodegenerative disorders like Alzheimer's or Parkinson's diseases. Previously, prion infections were shown to cause spongiform vacuolations, axonal swellings and accumulation of amyloid protein fibrils. Impaired axonal transport had not been observed so far. To monitor the axonal transport, Ermolayev and co-authors injected special dyes into mouse motor neurons, using a combination of confocal and novel ultramicroscopy techniques to monitor the dye delivery to the neurons and characterize the functional properties of axonal transport.

After prion injection into the brain and motor neuron system, Ermolayev and colleagues observed the described clinical symptoms. When clinical symptoms occurred, the researchers found a clearly reduced axonal transport in the neurons of two brain centers, the red nucleus and the motor cortex. Axonal transport impairments were seen in 45 per cent of neurons in the red nucleus and up to 94 per cent of motor cortex neurons.

"These results will help us to find better ways for diagnosis and treatment of prion diseases," says Dr. Vladimir Ermolayev.

This research was funded by the German Research Foundation (DFG) to E.F. (Emmy Noether Program FL387/1-2), to M.K. and E.F. (SFB581, TP-A6), and to G.H. (FZ-82), and by the European Commission, 6th Framework Program, to T.C. (ZNIP-037783).

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Journal Reference:

1. Ermolayev et al. Impaired Axonal Transport in Motor Neurons Correlates with Clinical Prion Disease. PLoS Pathogens, 2009; 5 (8): e1000558 DOI: 10.1371/journal.ppat.1000558

 North Carolina State University researchers have discovered a link between copper and the normal functioning of prion proteins, which are associated with transmissible spongiform encephalopathy diseases such as Cruetzfeldt-Jakob in humans or "mad cow" disease in cattle. Their work could have implications for patients suffering from these diseases, as well as from other prion-related diseases such as Alzheimers or Parkinson's.

Prion proteins, or PrPs, are commonly found in brain tissue and throughout the central nervous system. In humans or animals with prion diseases, these proteins deform and aggregate, creating clumps of PrPs that interfere with the nervous system's ability to function normally. A team of NC State physicists, led by Miroslav Hodak and Jerry Bernholc, has found that when PrPs bind with copper in the human body, their structure becomes more stable and less likely to misfold or aggregate.

"We believe that a prion protein's normal function is to serve as a copper buffer in the human body, binding with copper ions and keeping those ions from damaging human tissue," Hodak says. "We wanted to determine whether this was the normal function of the prion, and then look at how that binding affected the prion's structure."

The researchers created a 3-D model of the PrP using supercomputers at Oak Ridge National Laboratories. With the model, they determined that PrPs can bind up to four copper ions apiece, depending on the concentration of copper present. They also found that when the PrPs bind to the copper ions, the structure of the protein changes, becoming more stable.

"Prion proteins are unusual in that half of the protein has a well-defined structure, but the other half of it – where the binding occurs – is a flexible, random tangle," Hodak says. "When we looked at the so-called 'random' portion of the PrP where that binding occurs, we found that the copper ions lend stability to the overall protein. This stability may play a role in preventing PrPs from misfolding or aggregating – which indicates that with prion diseases, copper binding may be beneficial."

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Journal Reference:

1. Miroslav Hodak, Robin Chisnell, Wenchang Lu and Jerry Bernholc. Cu2 Binding to the Prion Protein: Functional Implications and the Role of Copper. Proceedings of the National Academy of Sciences, June 22, 2009

— Scientists at the National Institutes of Health have gained a major insight into how the rogue protein responsible for mad cow disease and related neurological illnesses destroys healthy brain tissue.

"This advance sets the stage for future efforts to develop potential treatments for prion diseases or perhaps to prevent them from occurring," said Duane Alexander, M.D., Director of NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), where the study was conducted.

The researchers discovered that the protein responsible for these disorders, known as prion protein (PrP), can sometimes wind up in the wrong part of a cell. When this happens, PrP binds to Mahogunin, a protein believed to be essential to the survival of some brain cells. This binding deprives cells in parts of the brain of functional Mahogunin, causing them to die eventually. The scientists believe this sequence of events is an important contributor to the characteristic neurodegeneration of these diseases.

The findings were published in the current issue of the journal Cell. The study was conducted by Oishee Chakrabarti, Ph.D. and Ramanujan S. Hegde, M.D., Ph.D., of the NICHD Cell Biology and Metabolism Program.

Central to prion diseases like mad cow disease and to many other diseases is the phenomenon known as protein misfolding, Dr. Hegde explained. Proteins are made up of long chains of molecules known as amino acids. When proteins are created, they must be carefully folded into distinct configurations. The process of protein folding is analogous to origami, where a sheet of paper is folded into intricate shapes. Upon correct folding, proteins are transported to specific locations within cells where they can perform their various functions. However, the protein chains sometimes misfold. When this happens, the incorrectly folded protein takes the wrong shape, cannot function properly, and as a consequence, is sometimes relegated to a different part of the cell.

In the case of prion diseases, the culprit protein that misfolds and causes brain cell damage is PrP. Normally, PrP is found on the surface of many cells in the body, including in the brain. However, the normal folding and distribution of PrP can go wrong. If a rogue misfolded version of PrP enters the body, it can sometimes bind to the normal PrP and "convert" it into the misfolded form.

This conversion process is what causes mad cow disease, also known as bovine spongiform encephalopathy. Feed prepared from cattle tissue containing an abnormally folded form of PrP can infect cows. In very rare instances, people eating meat from infected cows are thought to have contracted a similar illness called variant Creutzfeld Jacob disease (vCJD). In other human disorders, genetic errors cause other abnormal forms of PrP to be produced.

"The protein conversion process has been well studied," Dr. Hegde said. "But the focus of our laboratory has been on how — and why — abnormal forms of PrP cause cellular damage."

To investigate this problem, Dr. Hegde’s team has been studying exactly how, when, and where the cell produces abnormal forms of PrP. They had found that many of the abnormal forms of PrP were located in the wrong part of the cell. Rather than being on the cell’s surface, some PrP is exposed to the cytoplasm, the gelatinous interior of the cell. Moreover, several studies from Dr. Hegde’s group and others showed that when too much of a cell’s PrP is exposed to the cytoplasm in laboratory mice, they develop brain deterioration.

"The sum of these discoveries provided us with a key insight," Dr. Hegde said. "We realized that in at least some cases, PrP might be inflicting its damage by interfering with something in the cytoplasm."

In the current study, Drs. Chakrabarti and Hegde sought to determine what went wrong when PrP was inappropriately exposed to the cytoplasm. Their next clue came from a strain of mice with dark mahogany-colored fur. Although these mice develop normally at first, parts of their nervous systems deteriorate with age. Upon autopsy, their brains are riddled with tiny holes, and have the same spongy appearance as the brains of people and animals that died of prion diseases. The gene that is defective in this strain of mice is named Mahogunin.

"The similarity in brain pathology between the Mahogunin mutant mice and that seen in prion diseases suggested to us that there might be a connection," Dr. Hegde said.

To investigate this possible connection, the researchers first analyzed PrP and Mahogunin in cells growing in a laboratory dish. When the researchers introduced altered forms of PrP into the cytoplasm of cells, they saw that Mahogunin molecules in the cytoplasm bound to the PrP, forming clusters. This clustering led to damage in the cell that was very similar to the damage occurring when cells are deprived of Mahogunin.

The researchers found that this damage did not occur in the cell cultures if PrP was confined to the surface of the cell, if the cells were provided with additional Mahogunin, or if PrP was prevented from binding to Mahogunin.

The researchers then studied mice with a laboratory induced version of a human hereditary prion disorder called GSS, or Gerstmann-Straussler-Scheinker Syndrome. This extremely rare disease causes progressive neurological deterioration, typically leading to death between age 40 to 60. Dr. Hegde explained that some GSS mutations result in a form of PrP that comes in direct contact with the cytoplasm. In mice that contain one of these mutations, the researchers discovered that cells in parts of the brain were depleted of Mahogunin. The researchers did not see this depletion if PrP was engineered to avoid the cytoplasm.

The findings, Dr. Hedge said, strongly suggest that altered forms of PrP interfere with Mahogunin to cause some of the neurologic damage that occurs in prion diseases.

"PrP probably interferes with other proteins too," Dr. Hegde said. "But our findings strongly suggest that the loss of Mahogunin is an important factor."

An understanding of how PrP interacts with Mahogunin sets the stage for additional studies that may find ways to prevent PrP from entering the cytoplasm, or to replace Mahogunin that has been depleted.

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Journal Reference:

1. Oishee Chakrabarti, Ramanujan S. Hegde. Functional Depletion of Mahogunin by Cytosolically Exposed Prion Protein Contributes to Neurodegeneration. Cell, 2009; 137 (6): 1136 DOI: 10.1016/j.cell.2009.03.042

— Imbalance of iron homeostasis is a common feature of prion disease-affected human, mouse, and hamster brains, according to a new study by Dr. Neena Singh and colleagues at Case Western Reserve University School of Medicine, alongside collaborators from Creighton University.

These findings provide new insight into the mechanism of neurotoxicity in prion disorders, and novel avenues for the development of therapeutic strategies.

Unlike other neurodegenerative conditions, prion disorders are sporadic, inherited, and infectious, and affect both humans and animals; common examples are mad cow disease in cattle, scrapie in sheep, and Creutzfeldt-Jakob disease in humans. The causative agent is a misfolded protein referred to as PrP-scrapie that replicates itself by changing the conformation of neighboring copies of the same protein, namely the prion protein. Aggregates of PrP-scrapie are toxic to brain cells and cause a spongy-like appearance in diseased brains.

Research from the Singh laboratory suggests that accumulation of PrP-scrapie alters the metabolism of iron in diseased brains. The imbalance of brain iron homeostasis worsens with disease progression, and is not an outcome of end-stage disease. Since iron is highly toxic when mismanaged, this condition is likely to contribute significantly to prion-disease-associated neurotoxicity. The likely cause of this condition is loss of normal function of the prion protein in cellular iron metabolism demonstrated recently by Singh and colleagues, combined with gain of toxic function by the redox-active PrP-scrapie complex as shown in this report.

Singh and her team were surprised to find that prion disease-affected brains are iron deficient despite a significant increase in their overall iron content. The group concludes that ferritin, a major iron storage protein, co-aggregates with PrP-scrapie in diseased brains and sequesters bound iron in the complex, creating a state of apparent iron deficiency. The brain cells respond to this condition by increasing their level of iron uptake, thus creating a vicious cycle of increased iron uptake in the presence of increased iron.

These observations contribute to our understanding of how the prion agent causes neurotoxicity, and may enable the development of novel therapeutic strategies targeted at restoring brain iron homeostasis in prion disorders.

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Journal Reference:

1. Singh et al. Abnormal Brain Iron Homeostasis in Human and Animal Prion Disorders. PLoS Pathogens, 2009; 5 (3): e1000336 DOI: 10.1371/journal.ppat.1000336

— Scientists at the University of Liverpool have determined the atomic structure of the 'binding' between a brain protein and an antibody that could be key to treating patients with diseases such as variant CJD.

Variant Creutzfeldt-Jakob Disease (vCJD) is part of a family of rare progressive neurodegenerative disorders, called prion diseases, which affect both animals and humans. It is thought that those who have developed vCJD became infected through the consumption of cattle products contaminated with Bovine Spongiform Encephalopathy (BSE) – a brain disorder in cows, commonly known as Mad Cow Disease.

Prion diseases can develop when a naturally occurring brain prion protein called, PrP, comes into contact with infectious prions. This converts PrP into a form that has a different shape, and eventually leads to a build-up of protein in the brain, causing brain cells to die. It is thought that immunisation with antibodies that can 'stick' to PrP could treat and even prevent the development of the disease.

To understand the 'connection' between the antibody and the protein, scientists at Liverpool used X-ray crystallography technology to build a three-dimensional picture of the binding between an antibody called ICSM18 – designed to 'stick' effectively to prion proteins – and PrP cells.

Samar Hasnain, Professor of Molecular Biophysics at the University, explains: "To pin-point where the antibody 'sticks' to the protein we used X-ray crystallography, pioneered by Nobel Prize winner Max Perutz. Significantly we found that the point at which the protein and antibody came together was also where scientists at the Medical Research Council (MRC) Prion Unit had identified a single amino acid, which we now know has a significant impact on a patient's susceptibility to prion disease."

Scientists at the MRC Prion Unit, University College London, who collaborated on the research, have found that ICSM18 could help prevent brain cells from becoming infected as well as reverse early damage caused by the disease.

Professor John Collinge, Director of the MRC Prion Unit, added: "We have shown that ICSM18 has the highest therapeutic potential in animal and cell based studies, but we have yet to establish its impact on people who have vCJD or other prion diseases. We are currently working, however, to make human versions of the antibodies for future trials in people."

The research is funded by the Medical Research Council and is published in Proceedings of the National Academy of Sciences (PNAS.)

Background on vCJD

• Variant CJD was first reported in 1996 and more than 200 patients from 11 countries have now been diagnosed with the disease.
• The incubation period for vCJD is unknown because it is a new disease, but it is likely that a person who has consumed a BSE-contaminated product will develop the disease a decade or more later.
• The median age at death of patients with vCJD in the UK is 28 years.

Yale researchers have filled in a missing gap on the molecular road map of Alzheimer's disease.

In the Feb. 26 issue of the journal Nature, the Yale team reports that cellular prion proteins trigger the process by which amyloid-beta peptides block brain function in Alzheimer's patients.

"It has been a black box," said Stephen M. Strittmatter, senior author of the study and the Vincent Coates Professor of Neurology and director of Cellular Neuroscience, Neurodegeneration and Repair at the Yale School of Medicine. "We have known that amyloid-beta is bad for the brain, but we have not known exactly how amyloid-beta does bad things to neurons."

After an extensive gene expression analysis, the first step in amyloid-beta damage appears to involve cellular prion proteins. These proteins are normally harmless and exist within all cells, but on rare occasions they change shape and cause notorious prion diseases such as Creutzfeldt- Jacob disease, or its well-known variant, mad cow disease.

When the Yale team searched hundreds of thousands of candidates for potential disease-mediating receptors for the specific amyloid-beta form known to play a role in the development of Alzheimer's disease, the most likely candidate was cellular prion proteins. It seems that amyloid-beta peptides latch onto these cellular prion proteins and precipitate the damage in brain cells.

"They start the cascade that make neurons sick" said Strittmatter, a member of the Kavli Institute for Neuroscience.

Since these cellular prion proteins act at an early stage of disease development, the receptors make a promising target for new Alzheimer's therapies, Strittmatter said.

The study does not suggest that the conversion of cellular prion proteins to an infectious agent occurs in Alzheimer's disease, Strittmatter noted. However, the Nature paper does suggest that the role of usually harmless cellular prion proteins in common neurodegenerative diseases should be studied more rigorously, he said.

Other members of the Yale team included Juha Lauren, David A. Gimbel, Haakon B. Nygaard, and John W. Gilbert.

This work was supported by research grants from the Falk Medical Research Trust and the National Institutes of Health.

 A comprehensive mouse model of inherited prion disease exhibits cognitive, motor, and neurophysiological deficits that bear a striking resemblance to the symptoms experienced by patients with the human version of "mad cow disease," Creutzfeldt-Jakob disease (CJD). The research, published by Cell Press in the November 26th issue of the journal Neuron, provides exciting insight into the mechanism of disease and may lead to the development of new therapeutic strategies for this devastating neurodegenerative disorder.

Mutation in the D178N/V129 prion protein (PrP) is associated with a subtype of CJD characterized by early cognitive impairment with memory deterioration, behavioral and motor abnormalities, electroencephalographic (EEG) changes, and specific neuropathological alterations. To date, only two transgenic models of inherited prion disease exist, which develop motor deficits but do not recapitulate the cognitive and neurophysiological abnormalities typical of CJD.

"We need experimental models with a broader spectrum of clinical signs for insight into the mechanisms of neuronal dysfunction and its evolution, and to identify earlier markers of clinical disease when therapeutic intervention may be effective," says senior study author Dr. Roberto Chiesa of the "Mario Negri" Institute for Pharmacological Research in Milan, Italy. Dr. Chiesa and colleagues developed a new transgenic mouse model of CJD expressing the mouse homolog of the D178N/V129 mutation.

The mice, called Tg(CJD) mice, show motor symptoms, but also memory impairment and neurophysiological deficits, specifically EEG abnormalities and sleep alterations, strikingly similar to those observed in a CJD patient with the same mutation. The researchers also observed several neuropathological abnormalities in the Tg(CJD) mice, including alterations in the endoplasmic reticulum (ER), the neuronal protein trafficking machinery, and an associated intracellular retention of mutant PrP. This suggests that ER dysfunction might contribute to CJD pathology.

These findings demonstrate that Tg(CJD) mice faithfully mirror clinical and pathological symptoms associated with CJD. "Our results establish the first animal model of a genetic prion disease recapitulating cognitive, motor, and neurophysiological abnormalities of the human disorder," explains Dr. Chiesa. "This new model allows in-depth analysis of the disease mechanisms and may be useful for testing potential therapies for inherited prion diseases."

The researchers include Sara Dossena, Dulbecco Telethon Institute, Milan, Italy, "Mario Negri" Institute for Pharmacological Research, Milan, Italy; Luca Imeri, University of Milan Medical School, Milan, Italy; Michela Mangieri, Anna Garofoli, Dulbecco Telethon Institute, Milan, Italy, "Mario Negri" Institute for Pharmacological Research, Milan, Italy; Loris Ferrari, Dulbecco Telethon Institute, Milan, Italy, University of Milan Medical School, Milan, Italy; Assunta Senatore, Dulbecco Telethon Institute, Milan, Italy, "Mario Negri" Institute for Pharmacological Research, Milan, Italy; Elena Restelli, Dulbecco Telethon Institute, Milan, Italy, "Mario Negri" Institute for Pharmacological Research, Milan, Italy; Claudia Balducci, "Mario Negri" Institute for Pharmacological Research, Milan, Italy; Fabio Fiordaliso, "Mario Negri" Institute for Pharmacological Research, Milan, Italy; Monica Salio, "Mario Negri" Institute for Pharmacological Research, Milan, Italy; Susanna Bianchi, University of Milan Medical School, Milan, Italy; Luana Fioriti, Dulbecco Telethon Institute, Milan, Italy, "Mario Negri" Institute for Pharmacological Research, Milan, Italy; Michela Morbin, "Carlo Besta" National Neurological Institute, Milan, Italy; Alessandro Pincherle, "Carlo Besta" National Neurological Institute, Milan, Italy; Gabriella Marcon, "Carlo Besta" National Neurological Institute, Milan, Italy, University of Udine, Udine, Italy; Flavio Villani, "Carlo Besta" National Neurological Institute, Milan, Italy; Mirjana Carli, "Mario Negri" Institute for Pharmacological Research, Milan, Italy; Fabrizio Tagliavini, "Carlo Besta" National Neurological Institute, Milan, Italy; Gianluigi Forloni, "Mario Negri" Institute for Pharmacological Research, Milan, Italy; and Roberto Chiesa, Dulbecco Telethon Institute, Milan, Italy, "Mario Negri" Institute for Pharmacological Research, Milan, Italy.

The cause of diseases such as BSE in cattle and Creutzfeld–Jakob disease in humans is a prion protein. This protein attaches to cell membranes by way of an anchor made of sugar and lipid components (a glycosylphosphatidylinositol, GPI) anchor. The anchoring of the prions seems to have a strong influence on the transformation of the normal form of the protein into its pathogenic form, which causes scrapie and mad cow disease.

A team headed by Christian F. W. Becker at the TU Munich and Peter H. Seeberger at the ETH Zurich has now “recreated” the first GPI-anchored prion in the laboratory. As they report in the journal Angewandte Chemie, they have been able to develop a new general method for the synthesis of anchored proteins.

The isolation of a complete prion protein that includes the anchor has not yet been achieved, nor has it been possible to produce a synthetic GPI-anchored protein. The function of the GPI anchor has thus remained in the dark. A new synthetic technique has now provided an important breakthrough for the German and Swiss team of researchers.

The sugar component of natural prion GPI anchors consists of five sugar building blocks, to which further sugars are attached through branches. Details of the lipid component have not been determined before. As a synthetic target, the researchers thus chose a construct made of the five sugars and one C18-lipid chain and worked out the corresponding synthetic route. First, the anchor was furnished with the sulfur-containing amino acid cysteine. The prion protein was produced with the use of bacteria and was given an additional thioester (a sulfur-containing group). The centerpiece of the new concept is the linkage of the protein and anchor by means of a native chemical ligation, in which the cysteine group reacts with the thioester. This allowed the prion protein to firmly attach to the vesicle membranes by way of the artificial anchor.

This new concept will allow production of sufficient quantities of proteins modified with GPI anchors for in-depth studies. Experiments with the artificial GPI prion protein should help to clarify the influence of membrane association on conversion of the protein into the pathogenic scrapie form. This should finally make it possible to track down the infectious form of the prion.

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Journal Reference:

1. Becker et al. Semisynthesis of a Glycosylphosphatidylinositol-Anchored Prion Protein. Angewandte Chemie International Edition, 2008; DOI: 10.1002/anie.200802161