Work done in the lab of Prof. Samrat Mukhopadhyay, Indian Institute of Science Education and Research (IISER), Mohali
About author
Sayanta Mahapatra belongs to the Paschim Medinipur district in the state of West Bengal. He completed his graduation (B.Sc) in chemistry major from the S. A. Jaipuria College, Kolkata under the University of Calcutta. Then, he joined the Department of Biophysics and Biochemistry at the University of Kalyani, Kalyani, West Bengal to pursue a Master’s degree in biochemistry. In 2016, he joined the Department of Biological Sciences at IISER Mohali to pursue his Ph.D. under the supervision of Prof. Samrat Mukhopadhyay. In the Mukhopadhyay Lab, he is studying amyloid formation, disaggregation, and several molecular regulators of amyloid transmission using atomic force microscopy (AFM), steady-state fluorescence spectroscopy, and classical biochemical tools and techniques. Outside his scientific pursuits, he likes to travel and listen to music of different genres.
A molecular chaperone that generates adequate amyloid particles for cell-to-cell amyloid transmission
Interview
How would you explain your research outcomes to the non-scientific community?
Proteins are the most important biomolecules involved in many biological functions in cells. In your high school textbooks, we have learned that every newly synthesized protein folds into a three-dimensional shape to perform its particular function. However, the paradigm has shifted recently due to the discoveries of intrinsically disordered proteins or proteins that harbor disordered domains that are associated with flexible functions due to having dynamic ever-changing shapes instead of fixed shapes. These interesting classes of proteins along with the misfolded or unfolded structured proteins often tend to form polymers of proteins known as amyloids. Although these proteinaceous assemblies are classically linked with fatal neurodegenerative disorders, examples of their functional roles are not so rare . Recruitment of monomers to the pre-existing amyloids known as seeds accelerates protein aggregation, which is otherwise a slow process. Prions are the self-perpetuating sub-class of amyloids that drive amyloid transmission to neighbor cells through the formation of amyloids templated by preformed aggregates acting as seeds. The prion-like transmission via seeded generation of aggregates is currently thought to be the principal mechanism of amyloid spread for typical non-prion amyloids as well.
There is a pivotal class of proteins known as chaperones that ensures proper protein folding by preventing or reversing their misfolding or unfolding that might otherwise cause protein aggregation. However, despite all the surveillance, proteins, especially the ones with intrinsic disorders, form amyloids in altered cellular microenvironments. Therefore, there is an interesting class of chaperones in cells classified as disaggregases that try to solubilize already formed aggregates. The proper cellular level of disaggregase is critical for prion-like amyloid transmission as it creates adequate highly-transmissible lower order seeds upon disaggregation of higher-order amyloids that possess limited transmissibility. For our work, we used the yeast disaggregase Hsp104 to understand the dose-dependent remodeling of amyloids by disaggregases in the context of amyloid transmission. For our work via in vitro recapitulation, we used low amounts of pure Hsp104 to mimic the cellular scenario of disaggregase insufficiency during aging. We choose yeast functional prion Sup35 as a model amyloidogenic substrate that shares generic superstructural features with several neuropathological amyloids.
Our results show that the low concentration of Hsp104 can accelerate amyloid formation but can delay their conversion into higher-order aggregates such as fibrils. These alternations in aggregation behavior ensure the abundance of ample fibril precursors as seeds, which otherwise readily convert into less transmissible fibrils. Additionally, the amyloids generated in the presence of low concentrations of Hsp104 showed better potential to seed further amyloid generation and may efficiently carry forward amyloid infection to the recipient cells. Taken together, our data shed light on how disaggregase insufficiency during aging may promote amyloid colonization by creating seeding-efficient highly transmissible amyloids.
How do these findings contribute to your research area?
Several reports showed that chaperones either facilitate or hinder amyloid fibril formation. However, our study is probably the first report where we have shown the tug of war between the polymerization of the monomeric units leading to the formation of long thread-like fibrils and a chaperone at low concentrations that is trying to depolymerize them. This tussle ensures the prolonged persistence and spread of the fibril precursors that are believed to be the main culprits of neuropathology. In the absence of chaperones, these precursors readily convert into comparatively benign matured fibrils. Intriguingly, our work also indicated a nano-structural change in the aggregates generated in the presence of the disaggregase that lead to an increase in their ability to produce copies of themselves.
“Our work indicated a nano-structural change in the aggregates generated in the presence of the disaggregase that lead to an increase in their ability to produce copies of themselves.”
What was the exciting moment during your research?
Our characterization of amyloids formed in the presence of the disaggregase was continuously pointing toward the structural distinctness of these amyloids compared to those generated in the absence of any chaperone. The most exciting moment of our work was when these structurally distinct amyloids as seeds exhibited a significantly better ability to accelerate fresh aggregation reactions. These results unmasked the direct impact of chaperone-directed structural alterations in amyloids that may facilitate their transmission by facilitating the seeded amyloid formation, which we were anticipating for a long time.
What do you hope to do next?
In our lab, we will be extending this work by exploring the role of other co-chaperones of Hsp104 in its substrate processing and their possible implications in generating seeds for amyloid transmission. I have already submitted my thesis in the last month. Currently, I am looking for postdoctoral opportunities where I want to dig deep into the protein quality control system and its role in remodeling several neurodegenerative amyloids in vivo.
Where do you seek scientific inspiration from?
The principal source of my inspiration is the constant belief that even the darkest night will end and the sun will rise. Apart from that, my PI and highly motivated lab colleagues are my sources of scientific inspiration.
How do you intend to help Indian science improve?
I want to return to India after completing my postdoctoral stint in foreign institutes and set up my lab as a principal investigator in an Indian university or institute to pursue research on basic science.
Reference
Mahapatra, S., Sarbahi, A., Madhu, P., Swasthi, H. M., Sharma, A., Singh, P., & Mukhopadhyay, S. (2022). Substoichiometric Hsp104 regulates the genesis and persistence of self-replicable amyloid seeds of Sup35 prion domain. The Journal of biological chemistry, 298(8), 102143. https://doi.org/10.1016/j.jbc.2022.102143
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