Exploring the Structural Order of Condensates Formed by the PRD2 Domain of Mouse CPEB3

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 play 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 mouse CPEB3. Here, we have investigated the aggregation properties and the structural characteristics of the mouse PRD2 (mPRD2) in vitro. We found that mPRD2 undergoes phase separation at very low concentrations. Interestingly, mPRD2 formed stable, 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 the condensates. We propose that the distinct phase separation behavior of mPRD2 would be due to the conformational changes attributed to the pattern of the mPRD2 amino acid sequence, resulting in the formation of rigid, amyloid-like self-assembly.