The Cryo-EM structure of AAV2 Rep68 in complex with ssDNA reveals a malleable AAA+ machine that can switch between oligomeric states.

The adeno-associated virus (AAV) Rep proteins use a unique AAA+ domain to catalyze DNA replication, transcription regulation, and genome packaging. Also, they mediate site-specific integration during a latent phase. To understand the mechanisms underlying AAV Rep function, we investigated the cryo-EM and X-ray structures of Rep68-ssDNA complexes. Surprisingly, Rep68 generates hybrid ring structures where the Origin-Binding-Domain (OBD) forms octameric rings while the helicase domain (HD) forms heptamers. Moreover, the binding to ATPγS promotes a large conformational change in the entire AAA+ domain that leads the HD to form both heptamers and hexamers. The HD oligomerization is driven by an interdomain linker region that acts as a latch to catch the neighboring HD subunit and is flexible enough to permit the formation of different stoichiometric ring structures. Overall, our studies show the structural basis of AAV Rep structural flexibility required to fulfill its multifunctional role during the AAV life cycle.