Phase separation of second prion domain of CPEB3: Insights from the aggregation and structural studies

The maintenance of long-term memory requires sustainable synaptic connections, mediated by the prion-like transformation of the translational regulator protein CPEB3 (Cytoplasmic Polyadenylation Element Binding protein isoform 3) in mammals. The N- terminal prion domain of CPEB3, composed of the two prion subdomains PRD1 and PRD2 has previously been demonstrated to perform a crucial role in imparting prion-like properties to the protein. We have already reported the amyloid-core of the first prion subdomain (PRD1) of the mouse CPEB3. Here, we have investigated the aggregation properties and the structural characteristics of the mouse PRD2 (mPRD2) in vitro. We found that the mPRD2 undergoes phase separation. Interestingly, the mPRD2 formed stable and amyloid-like solid condensates instead of the typical liquid condensate formation. Solid-state NMR and other biophysical studies revealed the existence of mixed secondary structures for mPRD2 in condensates. We propose that the distinct phase separation behaviour of the mPRD2 would be due to the conformational changes attributed to the pattern of the mPRD2 amino acid sequence, resulting in the formation of rigid and amyloid-like self-assembly.