Structural basis for Rep-mediated adeno-associated virus packaging

Adeno-associated viruses (AAVs) are parvoviruses utilized as gene therapy vectors. However, the AAV packaging mechanism is unresolved at the molecular level, creating a bottleneck for vector manufacturing, safety, and efficacy. Here, cryo-EM structures of the Rep helicase packaging motor in complex with the packaging marker DNA (ITR) and the Rep-AAV8 capsid complex are presented. Rep-ITR complexes reveal dynamic oligomeric states on the DNA, elucidating the strand separation mechanism coupled to its ATPase cycle. We observe Rep preferentially bound to empty capsids, with a binding interface likely conserved across the virus family. This complex also unveils a cryptic capsid ATP-binding site which, alongside Rep binding, triggers structural rearrangements priming the capsid for packaging. Collectively, these findings advance the understanding of Rep-mediated packaging, with significant implications for parvovirus virology and viral vector design.