20 21 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 The atomic structure of alpha-synuclein filaments of Parkinson’s disease Neurodegenerative Diseases – Non-Communicable Diseases – Health &Wellbeing – Neurology – Structural Biology – Life Sciences & Biotech Parkinson’s disease is a neurodegenerative disorder that affects millions of people around the world. It is a chronic and progressive disease that primarily affects the motor system, causing a range of symptoms such as tremors, rigidity, and difficultywithmovement and balance. Although Parkinson’s disease is most commonly diagnosed in older adults, it can also affect younger people. In many neurodegenerative diseases, one or a few different proteins form aggregates, i.e . amyloid filaments, in the brain. In Parkinson’s disease, the amyloid filaments are made of the protein alpha-synuclein. For the past six years, it has been possible to determine the 3D atomic structures of amyloid filaments extracted from the brains of people who have died with a neurodegenerative disease, using cryo-Electron Microscopy (cryo-EM). During that time, many structures have been solved, including the structure of amyloid filaments of the protein tau from the brains of individuals with Alzheimer’s disease. However, the structures of the filaments from Parkinson’s disease remained unknown. One of the difficulties was that many of them do not twist, which leads to technical problems in the structure determination process. In this study, an international team of researchers solved the structure of alpha-synuclein filaments. They collected many electron microscope images at eBIC and sifted through them all to find the minority of the filaments that did twist. Besides looking at alpha-synuclein filaments from the brains of individuals with Parkinson’s disease, they also looked at alpha-synuclein filaments from the brains of individuals with dementia with Lewy bodies (DLB). Although these are two different diseases, they found that alpha-synuclein filaments from the two diseases are identical. They have named this α-synuclein structure the Lewy fold. This observation agrees with similar neuropathological features in these brains, i.e. the presence of Lewy bodies. The discovery that α-synuclein filaments have identical structures in both diseases indicates that they share a continuum. However, this is not the case for some other neurodegenerative disorders characterised by an abundance of α-synuclein filaments. The research group had previously examined the structures of filaments from multiple system atrophy (MSA) and found them to be vastly different from the Lewy fold. Knowledge of the structure of the alpha-synuclein filaments can be used to develop new molecules that could be useful in the clinic. For example, it may now be possible to use structure-based design to develop small molecules as new ligands for positron emission tomography (PET) specific for Lewy and MSA folds. Such ligands allow the presymptomatic detection of α-synuclein assemblies in brain tissues, which is crucial to early intervention. The results can also be used to develop better model systems of disease and will help to develop methods for producing α-synuclein filaments with structures identical to those in human brains. In the long term, this work could lead to the development of new therapies for both Parkinson’s disease and dementia with Lewy bodies. Related publication: Yang, Y. et al. Structures of α-synuclein filaments from human brains with Lewy pathology. Nature 610 , 791–795 (2022). DOI: 10.1038/s41586-022- 05319-3 Funding acknowledgement: MRC (MC_UP_A025_1013 to S.H.W.S. and MC_U105184291 to M.G.) Corresponding authors: Sjors Scheres, Medical Research Council Laboratory of Molecular Biology,
[email protected] Michel Goedert, Medical Research Council Laboratory of Molecular Biology,
[email protected]) Biological Cryo-Imaging Group eBIC Secondary structure elements in the Lewy and multiple system atrophy (MSA) folds. Understanding a protein that fuels bowel cancer Non-Communicable Diseases – Health &Wellbeing – Cancer – Biochemistry – Chemistry – Structural Biology – Biophysics – Drug Discovery – Life Sciences & Biotech Tankyrase is an important protein that regulates a wide range of processes relevant to cancer and other conditions, such as diabetes, neurodegeneration and fibrosis. It supports ‘Wnt signalling’, essential for cell division and development and maintaining stem cells. Tankyrase also controls other cell functions critical to cancer, including the maintenance of telomeres at the end of chromosomes. Therefore, tankyrase has received substantial attention as a potential drug target. Tankyrase is part of the‘PARP family’of proteins, and drugs blocking PARP1 are already in clinical use. However, tankyrase remains poorly understood, with scientists unsure of how the protein is switched on, how it functions and how to block it without causing unwanted side effects. Tankyrase self-assembles to form filamentous polymers, but how polymerisation contributes to tankyrase function and catalytic activity was unknown. Scientists at The Institute of Cancer Research in London used cryo-Electron Microscopy (cryo-EM) at eBIC to investigate the architecture of tankyrase filaments. In particular, they were keen to identify any potential contacts made by the catalytic domains, as these interactions may control the effect of polymerisation on tankyrase’s activity. Using helical reconstruction, they revealed the architecture of a tankyrase filament containing the polymerisation and catalytic domains. Surprisingly, the filament turned out to be a double helix, something they didn’t anticipate based on previous X-ray crystallography studies. Their results revealed extensive interactions between different domains of tankyrase, including those involving the catalytic domain. Based on subsequent biophysical, biochemical and cell-based studies, the researchers proposed that a polymerisation- induced allosteric switch regulates tankyrase’s catalytic functions. The scientists draw parallels between the activation mechanism of PARP1 and tankyrase for the first time. Similarly to PARP1, they suggest tankyrase works by being recruited to a specific site and‘self-assembling’, activating itself by clustering and changing its 3D structure. Although previous research has developed drugs that block tankyrase - in the hope of treating bowel cancer - they caused too many side effects to reach clinical trials. That's likely due to tankyrase being involved in such a wide range of processes, or essential functions of Wnt signalling in normal cells. This work provides novel insights into fundamental biological mechanisms but should also enable the development of novel tankyrase inhibitors and overcome the limitations of currently available molecules. Related publication: Pillay, N. et al. Structural basis of tankyrase activation by polymerisation. Nature 612 , 162–169 (2022). DOI: 10.1038/s41586-022- 05449-8 Funding acknowledgement: Cancer Research UK, initially through a Career Establishment Award Establishment Award (C47521/A16217), followed by a Programme Foundation Award (C47521/A28286) Wellcome Trust through an Investigator Award (214311/Z/18/Z) The Lister Institute of Preventive Medicine through a Lister Institute Research Prize Fellowship The Institute of Cancer Research. Corresponding author: Sebastian Guettler, The Institute of Cancer Research,
[email protected] The signalling protein tankyrase forms punctate structures in cells (left, tankyrase shown in green with nucleus in blue). These puncta appear as tankyrase self-assembles into chain-like fibres. Cryo- electron microscopy of the isolated tankyrase protein enabled researchers to decipher the molecular structure of these fibres (right) and learn how tankyrase is activated by self-assembly. Biological Cryo-Imaging Group eBIC