Phase separation modulates the functional amyloid assembly of human CPEB3

How functional amyloids are regulated to restrict their activity is poorly understood. The cytoplasmic polyadenylation element-binding protein 3 (CPEB3) is an RNA-binding protein that adopts an amyloid state key for memory persistence. Its monomer represses the translation of synaptic target mRNAs while phase separated, whereas its aggregated state acts as a translational activator. Here, we have explored the sequence-driven molecular determinants behind the functional aggregation of human CPEB3 (hCPEB3). We found that the intrinsically disordered region (IDR) of hCPEB3 encodes both an amyloidogenic and a phase separation domain, separated by a poly-A-rich region. The hCPEB3 amyloid core is composed by a hydrophobic region instead of the Q-rich stretch found in the Drosophila orthologue. The hCPEB3 phase separation domain relies on hydrophobic interactions with ionic strength dependence, and its droplet ageing process leads to a liquid-to-solid transition with the formation of a non-fibril-based hydrogel surrounded by starburst droplets. Furthermore, we demonstrate the differential behavior of the protein depending on its environment. Under physiological-like conditions, it can establish additional electrostatic interactions with dissolved ions, increases the stability of its liquid droplets and follows a condensation-based amyloid pathway. [Display omitted] •hCPEB3 amyloid core spans the hydrophobic region comprising residues 100-150.•hCPEB3 LLPS is driven by hydrophobic interactions with ionic strength dependence.•hCPEB3 IDR undergoes liquid-to-solid transition and forms hydrogels.•hCPEB3 droplet stability is based on additional electrostatic interactions.•hCPEB3 undergoes a condensation-based amyloid pathway in physiological-like conditions.