RNA Binding to CCRRM of PABPN1 Induces Conformation Change

Poly(A) Binding Protein Nuclear 1 (PABPN1) is a nuclear poly(A)-binding protein that is highly conserved in eukaryotes. It plays multifaceted roles in RNA processing and metabolism, with its dysregulation closely linked to various diseases. PABPN1 contains an alanine-rich N-terminus, a central coiled-coil domain (CC), a conserved RNA recognition motif (RRM) and a C-terminal extension. PABPN1 influences mRNA splicing and stability through its RNA-binding capabilities, thereby modulating gene expression. While PABPN1 is known to interact with RNA, the molecular mechanism underlying this interaction with RNA awaits further investigation. Here, we designed and purified a PABPN1 fragment encompassing the RNA-binding domain (CCRRM fragment, amino acids 114-254). Using a combination of 3D modeling, small-angle X-ray scattering (SAXS) and selective 2'-hydroxyl acylation analyzed by primer extension (SHAPE) assay, our result indicated that CCRRM exhibits a high affinity for poly(A) RNA, a moderate affinity for GU-rich and CU-rich sequences, and negligible binding to AU-rich and CA-rich sequences. RNA binding induces conformation change in the CC. These results suggest that PABPN1 could potentially be involved in cytoplasmic polyadenylation and may influence the regulation of mRNA translation and degradation, although further investigation is required to confirm this role.