The image on the cover of the June 4 issue of Biophysical Journal is a three-dimensional reconstruction of a super-resolution Airyscan confocal image of multiphasic condensates composed of two disorder-rich neuronal proteins, namely, tau and the prion protein, in the presence of RNA. Each of these proteins is doped with their corresponding labeled counterparts [tau, Alexa488 labeled (green); and prion, Alexa594 labeled (red)]. Here, because of the stronger affinity of the prion protein for RNA, tau droplets are seen to encapsulate prion droplets, giving rise to a hierarchical “condensate-within-condensate” morphology. The original image was recorded by Sandeep K. Rai and Roopali Khanna from Samrat Mukhopadhyay’s lab at the Indian Institute of Science and Research (IISER), Mohali, by using a ZEISS LSM 980 with Airyscan2.
In the Mukhopadhyay lab at IISER Mohali, we are interested in exploring the intriguing dynamic identities of intrinsically disordered proteins and regions that are responsible for their rapidly fluctuating conformations and allow them to participate in a range of biophysical processes, including phase separation and amyloid formation. Our research shows that the prion protein potentiates the phase separation of tau to form condensates enriched in both components, which could have potential implications in the overlapping pathophysiology of distinct neurodegenerative diseases characterized by the misfolded forms of different disordered proteins. Interestingly, the morphology of these mixed condensates can be finely tuned in the presence of RNA, leading to the formation of multiphasic assemblies.
Phase-separated assemblies, such as the nucleoli, Cajal bodies, and P-bodies, are emerging at the forefront of various cellular activities, owing to their ability to provide distinct chemical environments coupled with different biological functions. In this regard, the material properties and the internal architecture of such condensates become essential determinants of their function. The nucleolus, for instance, is perhaps the most-well-studied multilayered, phase-separated assembly. The complex internal architecture of the nucleoli, with each phase characteristically enriched in distinct crucial components, allows for their functioning. Using a minimalistic system, we were able to recapitulate the ability of biomacromolecules to form complex multilayered assemblies in vitro, which may contribute to our understanding of the biophysical principles underlying multiphasic condensation.
Our results directly demonstrate the role of multicomponent phase separation in forming multiprotein amyloid-like aggregates, providing mechanistic underpinnings of the relatively unexplored role of protein interactions between different, unrelated proteins in driving the interconnected etiology of different neurological disorders. We believe our work offers a mechanistic picture for studying the potential effects of phase separation in the aspects of disease and uncovers potentially novel molecular targets for drug discovery against neurodegenerative diseases. In addition, biological phase transitions can be extended to several arenas in both fundamental and translational research, ranging from potential broad-range implications in the origins of life to the fields of synthetic biology and drug delivery.
More details of our research can be found on our lab website: https://www.MukhopadhyayLab.org.
— Samrat Mukhopadhyay