Chromosome segregation in Archaea: SegA– and SegB–DNA complex structures provide insights into segrosome assembly

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Abstract
Genome segregation is a vital process in all organisms. Chromosome partitioning remains obscure in Archaea, the third domain of life. Here, we investigated the SegAB system from Sulfolobus solfataricus. SegA is a ParA Walker-type ATPase and SegB is a site-specific DNA-binding protein. We determined the structures of both proteins and those of SegA–DNA and SegB–DNA complexes. The SegA structure revealed an atypical, novel non-sandwich dimer that binds DNA either in the presence or in the absence of ATP. The SegB structure disclosed a ribbon–helix–helix motif through which the protein binds DNA site specifically. The association of multiple interacting SegB dimers with the DNA results in a higher order chromatin-like structure. The unstructured SegB N-terminus plays an essential catalytic role in stimulating SegA ATPase activity and an architectural regulatory role in segrosome (SegA–SegB–DNA) formation. Electron microscopy results also provide a compact ring-like segrosome structure related to chromosome organization. These findings contribute a novel mechanistic perspective on archaeal chromosome segregation.
Funding Information
  • Academia Sinica
  • Ministry of Science and Technology, Taiwan (107-2311-B-001-032-MY3, 107-2311-B-001-033-MY3, 106-2311-B-007-007-MY3, 107-2321-B-007-004, 108-2321-B-007-002, 109-2321-B-007-001)
  • Biotechnology and Biological Sciences Research Council (BB/M007839/1, BB/R006369/1)

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