Cryo-EM structures of holo condensin reveal a subunit flip-flop mechanism

Transport of DNA within cohesin involves clamping on top of engaged heads by Scc2 and entrapment within the ring by Scc3

“… ( A ) Cohesin tetramer (yeast, this study), ( B ) pentamer (human, 6WG3) ( Shi et al, 2020 ) and ( C ) condensin (yeast, 6YVU) ( Lee et al, 2020 ) are shown in two orientations (same or similar to Figures 7A and 8A ). …”

“…Processing of the linear DNA dataset using boxes large enough to cover entire cohesin complexes ( Supplementary file 1 , Materials and methods) revealed a significant subset of particles (~30%) that contained lower-resolution information about the conformation of the coiled coils and placement of the hinge ( Figure 7D & E ). Despite partial head-proximal unzipping of the coiled coils in this state, the reconstructed map clearly revealed a folded conformation reminiscent of apo condensin, a fraction of ATP-bound condensin ( Lee et al, 2020 ) and apo cohesin ( Bürmann et al, 2019 ). A folded state was also presumed to exist in the human cohesin structure where the HAWKS and the hinge interacted directly, but the coiled coils could not be resolved ( Shi et al, 2020 ).…”

Condensin complexes: understanding loop extrusion one conformational change at a time

“…A striking feature of recent H. sapiens and S. cerevisiae condensin structural work is a bend in the coiled coils ∼15 nm from the hinge [27,59]. This bend, referred to as the 'elbow', has also been observed in EM analysis and crosslinking data of S. cerevisiae and S. pombe cohesin and E. coli MukBEF SMC-Kleisin, and results in the hinge bending to contact the SMC arms near the ATPase domains [40,60].…”

“…While individual crystal structures have provided much needed molecular detail of subunit interfaces, full understanding of the mechanism requires structural information on the intact complex in different functional states. Recent work by Lee and Merkel et al [59] have begun to address this gap in knowledge by determining cryo-EM structures of S. cerevisiae condensin in the presence and absence of ATP. Despite using pentameric complexes for much of their analysis, only one HAWK domain is visible in each structure, suggesting the HAWKs are highly dynamic.…”

“…Overlay of the S. cerevisiae Apo condensin structures with NIPBL/SMC1/DNA from H. sapiens cohesin structure [39], suggest condensin could bind DNA in a similar manner (Figure 3B,C). While no structural data exist for Ycs4 directly binding to DNA, several evidences suggest that Ycs4 play a central role in condensin binding to DNA: a positively charged patch defines the Ycs4 putative DNA binding surface [59], Ycs4 is able to efficiently bind DNA in gel shift assays [34], and the H. sapiens condensin I Ycs4 equivalent, CAP-D2 is essential for chromosome formation in chromosome assembly assays [36], suggesting that this is essential in condensin binding to DNA.…”