Investigating the Oligomerization of TorsinA as a Means to Develop DYT1 Dystonia Therapeutics
Abstract
This proposal for the Fiscal Year 2017 Peer Reviewed Medical Research Program (PRMRP) addresses the Topic Area Dystonia. Dystonia is a movement disorder characterized by involuntary muscle contractions causing abnormal, often repetitive, movements, postures, or both. It is estimated that at least 250,000 people in the United States suffer from this incurable disease. Dystonia can be caused by different factors, including inheritance, but also, most relevant to the PRMRP, by traumatic brain injury, medication, and exposure to certain toxins. The most common form of generalized dystonia, DYT1, which affects the entire human body, is primarily the result of a seemingly marginal modification within the protein TorsinA. Over the 20 years since the discovery of the mutation, progress toward understanding this devastating disease has been slow. What we know is that TorsinA is a tiny motor protein inside every cell of the human body, but we do not yet know what this motor does and how it functions. So far, researchers assumed TorsinA to behave similar to other motors that have been studied previously, but it turns out that these similarities are much less pronounced than initially anticipated. Our proposal builds on the past 5 years of research in my lab, which significantly advanced knowledge about TorsinA. We were able to establish that TorsinA does not self-activate, as it was expected. Instead, TorsinA uses one of two additional proteins, called LAP1 or LULL1, to engage its motor. LAP1 and LULL1 are activators, an important element toward deciphering the biological role of TorsinA, Protein function is dictated by its structure. Therefore, biologists seek to determine the three-dimensional (3D) structure of their protein of interest. Traditionally, this is done using X-ray crystallography, a method with which proteins can be “seen” at atomic detail. This way, we were able to determine the 3D structures of TorsinA and of the diseased protein. This allowed us to reveal the subtle differences between the two proteins in exquisite detail. We were able to show that, due to a subtle change in the structure, the diseased protein cannot be activated anymore. And, perhaps more importantly, it also gave us a first clue as to how the diseased protein may be “repaired” by developing an appropriate drug. Recently, we made another unexpected observation, that is, that TorsinA can oligomerize to form long, filamenteous structures. These structures are not formed with the dystonia mutant, indicating yet another, possibly unique function for TorsinA. In the proposed research, we aim at characterizing these filamentous structures in atomic detail. We hypothesize that they hold essential information about Torsin function. Due to the specific nature of these assemblies, X-ray crystallography alone is not a suitable tool for the analysis. We will instead exploit the dramatic advances in cryo-electron microscopy (cryo-EM) to study these assemblies. Cryo-EM is about to revolutionize structural biology, and in recognition of this, three pioneers in the field were deservedly awarded this year’s Chemistry Nobel Prize. We will use this technology to characterize the TorsinA filaments at medium resolution, which will guide us to achieve high resolution in a tailor-fit hybrid approach that will exploit again X-ray crystallography and protein engineering. Now we know that TorsinA can polymerize to generate filaments, or, alternatively, bind its activators LAP1/LULL1. Both processes are blocked by the disease mutation, generating a distinct possibility for interference by drugs. The disease mutation is a subtle surface change on the protein that can potentially be rectified by an appropriate small molecule, thus possibly paving the way toward a therapeutic drug. We will screen for such drugs, setting up screening assays exploiting the two functional states of TorsinA that we have structurally characterized. We expect that t
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 29, 2018
- Source ID
- W81XWH1810515
Entities
People
- Thomas J. Schwartz
Organizations
- Massachusetts Institute of Technology
- United States Army