Structural basis for a PABPN1 aggregation-preventing antibody fragment in OPMD

Oculopharyngeal muscular dystrophy is caused by small alanine expansions in polyadenylate binding protein nuclear 1 (PABPN1) protein resulting in its intranuclear accumulation in skeletal muscle. 3F5 llama antibody specifically interferes with the PABPN1 aggregation process in vitro and in vivo. To understand the structural basis for its epitope recognition we mapped the binding interface of 3F5 with PABPN1 and provide a structural model of the 3F5-PABPN1 complex. We show that 3F5 complementarity determining regions create a cavity in which PABPN1 alpha-helix domain resides by involving critical residues previously implicated in the aggregation process. These results may increase our understanding of the PABPN1 aggregation mechanism and the therapeutic potential of 3F5.