Title : Single-molecule biophysical studies on genome organization by SMC proteins
일시 : 2022년 12월 6일(화), 17시
Speaker : 류제경(서울대학교)
Abstract : In each
human cell, 2 meter DNA is physically compacted into chromosomes that are
packed into a micrometer-sized nucleus, but the mechanism by which the
extremely long and negatively charged polymer is compacted into this tiny
structure remains elusive. Structural Maintenance of Chromosome (SMC) protein
complexes such as cohesin and condensin are the key organizers of the
spatiotemporal structure of chromosomes by extruding DNA loops1. In our
work using liquid-phase High-Speed Atomic Force Microscopy (HS AFM) and
magnetic tweezers (MT)1,2, we were
the first to obtain experimental data for yeast condensin acting on individual
DNA molecules. The findings suggest a scrunching model in which the SMC complex
extrudes a DNA loop by a cyclic switching of its conformation between open and
collapsed shapes. In addition, we show that yeast cohesin complexes
unexpectedly can exhibit a new type of phase separation, called a
Bridging-Induced Phase Separation (BIPS) that is induced by bridging of distant
regions on a long DNA by proteins that possess multiple DNA-binding sites3. Our
findings suggest that both DNA loop extrusion and phase separation by SMC
complexes are fundamental building blocks of chromosome organization.
References
1. Ryu, J.-K. et al. The condensin
holocomplex cycles dynamically between open and collapsed states. Nat.
Struct. Mol. Biol. 27, 1134–1141 (2020).
2. Ryu, J. K., Rah, S. H., Janissen, R., Kerssemakers, J. W.
J. & Dekker, C. Condensin extrudes DNA loops
in steps up to hundreds of base pairs that are generated by ATP binding events. Nucl. Acids Res.,
gkab1268, (2022).
3. Ryu, J.-K. et al. Bridging-induced phase separation
induced by cohesin SMC protein complexes. Sci. Adv. 7, eabe5905
(2021).