Kanazawa – November 04, 2026 -- Researchers at Kanazawa University and the National Institute of Genetics have recorded the Smc5/6 protein complex switching between two shapes to capture DNA, tether separate DNA sections and compact twisted strands. The team used high-speed atomic force microscopy (HS-AFM) and published the results in Nature Communications 17, 10398 (2026).
HS-AFM video shows Smc5/6 alternating between I-shaped and O-shaped forms
HS-AFM tracks molecular movements at the nanometre scale and records image sequences over time, unlike conventional methods that mainly provide static views. The team applied it to purified Smc5/6 from budding yeast under controlled laboratory conditions.
Smc5/6 adopted two distinct configurations. In the I-shaped form, its two long arms lay close together. In the O-shaped form, the arms separated into an open structure.
Adenosine triphosphate (ATP) influenced the transition. Binding ATP promoted the open configuration, while subsequent ATP-related changes were associated with different ways of holding DNA.
Smc5/6 grips DNA at two sites and tethers two separate sections
The images showed DNA held near regions at one end of the assembly in some configurations. In others, DNA sat inside the structure formed by the arms. The caption of the featured image describes head-binding and hinge-binding modes.
The researchers also observed Smc5/6 contacting two separate DNA sections simultaneously, holding them together in a process known as DNA tethering.
Twisted DNA occupies a smaller area when bound by Smc5/6
When Smc5/6 interacted with twisted DNA structures, the DNA covered a smaller area than DNA without the protein assembly. The results suggest Smc5/6 can contribute to DNA compaction by bringing sections together and stabilizing twisted arrangements.
"By observing individual Smc5/6 structures as they interacted with DNA, we could see how changes in their shape are associated with different ways of capturing and holding DNA," said Kenichi Umeda of Kanazawa University.
Experiments used purified proteins outside living cells and show no clinical application
The work examined purified Smc5/6 and DNA in vitro, so the images do not establish every step of Smc5/6 activity inside living cells. The authors state the study addresses fundamental molecular biology and does not demonstrate a medical treatment or clinical application. They say a better understanding of the mechanisms may eventually contribute to research on failures in DNA maintenance and repair.
Authors are Kenichi Umeda, Yumiko Kurokawa, Noriyuki Kodera and Yasuto Murayama. Funding came from the Japan Science and Technology Agency (PRESTO and CREST programs), the Japan Society for the Promotion of Science (KAKENHI grants), the Takeda Science Foundation and the World Premier International Research Center Initiative of Japan's Ministry of Education, Culture, Sports, Science and Technology.