DLS- Scientific Seminar Series: Special Research Talk on Biological Phase Separation: A New Phase in Biology

The Department of Life Sciences organizes a research seminar by Dr. Samrat Mukhopadhyay in its ‘Scientific Seminar Series’ on the topic "Biological Phase Separation: A New Phase in Biology". Dr. Mukhopadhyay’s broad research interest focuses on phase separation biology with most projects focusing on prions; amyloids; protein misfolding & aggregation. Further details are as follows-

He is a Professor of Biology and Chemistry at Indian Institute of Science Education and Research (IISER) Mohali, Punjab, India

Abstract: Living cells are like fully functional houses containing separate rooms dedicated to different activities. Similar to partition walls separating these rooms in a house, cells use membranes to compartmentalize cellular constituents into organelles. However, a growing body of fascinating research reveals there is also an alternative mechanism of intracellular organization. This is achieved through biomolecular condensation via liquid-liquid phase separation of highly flexible proteins, called intrinsically disordered proteins/regions (IDPs/IDRs), and nucleic acids into membrane-less organelles. Highly dynamic intracellular liquid-like condensates act as on-demand organelles that are formed and dissipated depending on the cellular requirements. Sometimes, these functional liquid droplets can undergo (irreversible) aberrant phase transitions into gel-like or solid-like aggregates associated with deadly human diseases. Therefore, delineating the molecular drivers of biological phase separation is essential to understating of cell physiology and disease. We discovered that the prion protein (PrP) (well-known for its association with mad cow disease and Creutzfeldt-Jakob disease) can undergo phase separation via weak, multivalent, transient intermolecular interactions between the N-terminal IDR that resembles a yeast prion-like domain. An intriguing disease-associated amber stop codon mutation (Y145Stop) of PrP yields a C-terminally truncated intrinsically disordered fragment. We demonstrated that Y145Stop spontaneously phase-separates into highly dynamic liquid droplets under physiological conditions (1). Upon aging, these highly dynamic liquid droplets undergo a liquid-to-solid phase transition into highly ordered, beta-rich, amyloid-like aggregates that exhibit a characteristic autocatalytic self-templating behavior. The propensity for the aberrant phase transition is much lower for the full-length PrP indicating an evolutionarily conserved role of the folded C-terminal domain (1,2). Our recent results also showed intriguing spatiotemporal modulations in complex coacervation of PrP with other neuronal IDPs into heterotypic, multi-component, multi-phasic, multi-layered condensates in the presence of RNA. These multi-component condensates can act as reaction crucibles to catalyze the amyloid conversion of these functional assemblies into pathological aggregates associated with overlapping neuropathological features (3,4). If time permits, I will also discuss our work on the characterization of biomolecular condensates using ultrasensitive surface-enhanced Raman scattering (5).

References

1. "An intrinsically disordered pathological prion variant Y145Stop converts into self-seeding amyloids via liquid-liquid phase separation". A. Agarwal, S.K. Rai, A. Avni & S. Mukhopadhyay. Proc. Natl. Acad. Sci. USA(2021) 118, 45, e2100968118. https://doi.org/10.1073/pnas.2100968118
2. "Prion Protein Biology Through the Lens of Liquid-Liquid Phase Separation". A. Agarwal & S. Mukhopadhyay. J. Mol. Biol.(2022) 434, 167368. https://doi.org/10.1016/j.jmb.2021.167368 
3. "Spatiotemporal Modulations in Heterotypic Condensates of Prion and α-Synuclein Control Phase Transitions and Amyloid Conversion" A. Agarwal, L. Arora, S.K. Rai, A. Avni & S. Mukhopadhyay. Nature Communications(2022) 13, 1154. https://www.nature.com/articles/s41467-022-28797-5
4. "Heterotypic electrostatic interactions control complex phase separation of tau and prion into multiphasic condensates and co-aggregates" S. K. Rai, R. Khanna, A. Avni & S. Mukhopadhyay. Proc. Natl. Acad. Sci. USA(2023) 120, e2216338120. https://doi.org/10.1073/pnas.2216338120 
5. "Single-Droplet Surface-Enhanced Raman Scattering Decodes the Molecular Determinants of Liquid-Liquid Phase Separation" A. Avni, A. Joshi, A. Walimbe, S. G. Pattanashetty & S. Mukhopadhyay. Nature Communications(2022) 13, 4378. https://www.nature.com/articles/s41467-022-32143-0