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Twists and Turns in Protein Assembly

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Twists and Turns in Protein Assembly Twists and Turns in Protein Assembly Professor Robert Fairman TWISTS AND TURNS IN PROTEIN ASSEMBLY In nerve cells, the accumulation of protein into bundles of insoluble fibres is the underlying cause of a number of neurodegenerative diseases. Professor Robert Fairman and his team at Haverford College are developing cutting edge techniques to unravel this process. Proteins are the building blocks of life. The leads to the death of particularly vulnerable genetic code within each cell of our bodies cells such as neurones – the elaborate and controls the sequence of molecules called sensitive cells in our brain. This is the basic amino acids, which assemble together mechanism that causes the debilitating and to form each protein. But this is only the currently untreatable neurological disorder first step. Amino acids are small charged Huntington’s disease, which is characterised molecules that interact with one another as by a disruption of normal movements and they join together to form strings of peptides a decline in mental ability, resulting in (polypeptides), which spontaneously develop dementia. into different structures known as secondary structures. This can involve the formation ‘The relationship of this aggregation to of sheets or helical spirals following certain disease is poorly understood, and differences rules determined by the order of the amino in protein structure may underlie differences acids. These secondary structures then in toxicity,’ Professor Fairman admits. ‘Many interact with one another to form larger neurodegenerative diseases (Alzheimer’s, tertiary structures of proteins that control Huntington’s, Parkinson’s) have a similar and mediate every aspect of cell function. underlying molecular mechanism of protein aggregation, involving the formation of ‘Ever since I was an undergraduate student, an extended polypeptide chain that can I’ve always been fascinated with a chemical aggregate through ß-sheet formation.’ view of biology,’ Professor Fairman tells As such, it is vital to understand how Scientia. He first became fascinated with these protein aggregates are formed and proteins and their structure during a the intermediary steps that lead to the research internship at Brookhaven National development of small fibres and larger Laboratories, where he worked on the structures that somehow disturb normal cell assembly of a virus that infects bacteria chemistry and function in neurones. called a bacteriophage. During his graduate studies, he became particularly interested in Professor Fairman’s team use the latest a quantitative approach to protein folding developments in a technique called and protein design, and says that, ‘much of analytical ultracentrifugation, which involves my work over my career has taken advantage spinning solutions of peptides at very high of protein design approaches to study speeds to separate them according to interesting problems in protein assembly.’ their sizes under the influence of elevated G-forces (gravity). More recently, they have Gumming Up the Works combined this technique with detecting specific proteins, which have been tagged Many genes encode long sequences of with fluorescent markers. ‘Our work takes the amino acid glutamine. Alterations advantage of a key biophysical method that in the DNA encoding these regions can allows for the study of protein aggregation lead to repetitions and an increase in the in solution, and more specifically, with the length of these sequences. When these use of fluorescence detection, allows such chains of glutamine become too long, characterisation in complex mixtures that protein aggregates can start to form. These better represent cellular conditions,’ says aggregates are formed from structures Professor Fairman. known as ß-sheets, which assemble into tiny fibres (fibrils) that cannot be dissolved. This WWW.SCIENTIA.GLOBAL ‘My collaborator, Tom Laue, and I are among a handful of people who are applying recent advances in fluorescence detection to study protein aggregation in complex mixtures. We’re confident that the development of this new technique will create new breakthroughs in understanding protein aggregation and its influence on disease.’ Assistance from Neighbours ‘This tool satisfies my innate interest in They went on to examine the appearance quantitative approaches to biology research.’ and structure of the fibres produced by In work published in 2010, Professor Using these techniques, Professor Fairman’s these synthesised peptides in order to Fairman’s team looked at the early team looked at how regions in the protein reveal the mechanisms that produce much assembly of these very small ß-sheet fibres known to cause Huntington’s disease could larger structures, from layers of ß-sheets, by synthesising their own small peptides, interact and mediate the formation of like those found in neurones. They observed containing repeating glutamines, that had aggregates. that the presence of the coiled-coil helical been engineered to spontaneously form into structure did not prevent ß-sheet structure a hairpin shaped structure. This approach One region with a helical structure in the from forming, but it reduced the bundling of produced observable fibres under the huntingtin protein, which is adjacent to fibres that produces these larger structures. microscope and provided a good model of the glutamine rich ß-sheets, is known to be Understanding these mechanisms behind the the intermediate steps in fibre production in important for the formation of aggregates. assembly of larger structures can facilitate neurodegenerative disease. This is especially In order to investigate the role this structure new approaches for designing inhibitors of important in light of the evidence that these plays in the process, this 17 amino acid protein aggregation. In addition, it allows early intermediate steps could be particularly long helical region was fused to a glutamine researchers to design peptides that favour toxic to cells, giving the team the chance to sequence. This same glutamine sequence particular shapes, in order to investigate how study how such structures assemble, and was fused to another previously well studied these different structures lead to cell death in uncover the cause of this toxicity. coiled-coil structure consisting of two both cells and animal models. helices or coils twisted together like a rope. Professor Fairman’s team published two Comparing the two allowed the team to test Glowing Worms further studies in 2014 that explored different models of how these regions of the assembly of protein aggregates in the protein interact with one another. The Fibres formed from ß-sheets can become Huntington’s disease, using analytical presence of the coiled-coil acted to reduce tangled together and can drag in other ultracentrifugation and electron microscopy. aggregation and supported the model that molecules within the cell to produce much ‘I have become fascinated with the use interaction between regions is an important larger structures called inclusion bodies. of the analytical ultracentrifuge as a factor in the formation of aggregates from In more recent work published in the last unique biophysical tool to study protein ß-sheets. year, the team have developed the use of aggregation,’ states Professor Fairman. WWW.SCIENTIA.GLOBAL analytical ultracentrifugation combined with a fluorescence detection open to the global community,’ Professor Fairman states. ‘It is exciting system to look at the intermediate steps in protein aggregation to be involved at the cutting edge of this technology, particularly and inclusion body formation in an animal. This is of fundamental bringing this approach to my teaching as well.’ Students have been importance to understanding which of these intermediate steps is toxic actively involved in work that has been published this year after or protective and contributes to cell death and disease. working on bacterial enzymes that synthesise biologically useful peptides like anti-bacterial agents. This work could aid the redesign of Advances in genetics now make it possible to label particular proteins such synthases for use in bioengineering projects. The teaching labs of interest with fluorescent markers. A commonly used system involves also provide students with a unique experience of the scientific process, genetically manipulating the worm Caenorhabditis elegans to allow as well as rigorous quantitative training in protein structure. visualisation of such proteins within the living animal. Professor Fairman’s team have shown that crude extracts from these worms Professor Fairman and his team plan to continue investigating the early can be analysed using ultracentrifugation methods to detect a wide steps in the aggregation of proteins with long glutamine sequences, range of intermediate aggregates of protein from the smallest fibres and the influence of flanking regions in animal models such as of ß-sheets to the larger inclusion bodies characteristic of neuronal Caenorhabditis elegans and the fly Drosophila melanogaster. Both of damage in humans. This is proof of the concept that this method can these model species can be genetically modified to label proteins of be used in a whole animal model of disease using complex mixtures interest with fluorescent markers, making them ideal candidates for the formed within a multi-cellular animal. The technique also allows the application of this technique. different types of intermediate aggregates of protein to be studied under the microscope
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