Submolecular video-imaging of the Smc5/6 complex topologically bound to DNA

Structural maintenance of chromosomes (SMC) complexes are ring-shaped ATPases that hold distinct DNA segments together to regulate various chromosome structures and functions. However, their dynamic mechanisms of DNA binding and processing remain poorly understood. Here, using high-speed atomic force microscopy, we directly visualized the dynamics of the Smc5/6 complex on DNA at submolecular resolution, resolving its individual domains. ATP-bound Smc5/6 stably binds DNA via the ATPase head domain, whereas following ATP hydrolysis, the DNA is entrapped within the SMC compartment and positioned around the opposite hinge domain. Furthermore, Smc5/6 topologically entraps two DNA segments together and stabilizes the DNA twist structures, promoting DNA compaction. Our findings provide a visual demonstration of how an SMC complex employs its ring architecture to facilitate distinct DNA binding modes.