Molecular Determinants of Liquid Demixing and Amyloidogenesis in Human CPEB3

The cytoplasmic polyadenylation element-binding protein 3 (CPEB3), is an RNA-binding protein which in its soluble state is localized in membraneless neuronal RNA granules keeping target mRNAs in a repressed state. The stimulus-dependent aggregation of CPEB3 activates target mRNAs translation, a central event for the maintenance of long-term memory-related synaptic plasticity in mammals. To date, the molecular determinants that govern both connected events remain unclear. Here, to gain insight into these processes, the biophysical properties of the human CPEB3 (hCPEB3) are characterized. We found that hCPEB3 homotypic condensation is mainly driven by hydrophobic interactions and occurs under physiological conditions. Moreover, hCPEB3 biomolecular condensates are dynamic inside living cells, whose localization and stabilization are mediated by its RNA-recognition domains. In contrast, the hCPEB3 polar N-terminal region is crucial for hCPEB3 amyloid-like aggregation , which is disrupted by the polyglutamine binding peptide 1 (QBP1), A seeds and Hsp70, highlighting the importance of the QRQ tract as well as the hydrophobic residues for hCPEB3 functional aggregation. Based on these findings, we postulate a model for hCPEB3’s role in memory persistence that advances a rather sophisticated control for hCPEB3 condensate dissociation and amyloid-like formation to achieve its physiological function.