An asymmetric SMC–kleisin bridge in prokaryotic condensin


Eukaryotic structural maintenance of chromosomes (SMC)–kleisin complexes form large, ring-shaped assemblies that promote accurate chromosome segregation. Their asymmetric structural core comprises SMC heterodimers that associate with both ends of a kleisin subunit. However, prokaryotic condensin Smc–ScpAB is composed of symmetric Smc homodimers associated with the kleisin ScpA in a postulated symmetrical manner. Here, we demonstrate that Smc molecules have two distinct binding sites for ScpA. The N terminus of ScpA binds the Smc coiled coil, whereas the C terminus binds the Smc ATPase domain. We show that in Bacillus subtilis cells, an Smc dimer is bridged by a single ScpAB to generate asymmetric tripartite rings analogous to eukaryotic SMC complexes. We define a molecular mechanism that ensures asymmetric assembly, and we conclude that the basic architecture of SMC–kleisin rings evolved before the emergence of eukaryotes.

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Figure 1: ScpA's winged-helix domain associates with Smc.
Figure 2: Organization of ScpAB.
Figure 3: Structure of a second SMC–kleisin interface.
Figure 4: A single ScpAB bridge connects Smc heads.
Figure 5: Architecture of Smc–ScpAB complexes in vivo.
Figure 6: Mechanisms promoting assembly of Smc2–ScpA–ScpB2 rings.
Figure 7: Model for the functional unit of the Smc–ScpAB holocomplex in cells.

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We thank E. Conti and S. Jentsch for sharing resources and helpful advice and K. Nasmyth and W. Zachariae for critical reading of the manuscript. We are grateful to the MPI Crystallization Facility for HTP screening, to the MPI Core Facility and C. Eberl for help with MS analysis, to M. Blettinger, A.-L. Cost and P. Ringer for technical help and to H. Murray (Newcastle University, Newcastle upon Tyne, UK) for providing DnaA protein and antiserum. S. Uebel kindly performed and analyzed the analytical ultracentrifugation experiments. We thank A. Pauluhn, V. Olieric and the staff of the PX beamlines at the Swiss Light Source (SLS, Villigen, Zurich) for assistance during crystallographic data collection and E. Lorentzen and R. Prabu for helpful advice for twinning refinement. We also acknowledge the use of Beamline 5C at PAL and BL41XU at the SPring-8. This work was supported by funding from the Max Planck Society and a Starting Grant from the European Research Council ERC StG #260853 “DiseNtAngle” (S.G.) and by the National Research Foundation of Korea grant 2012-0005612 (B.-H.O.).

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F.B., B. subtilis strain constructions and cellular and biochemical experiments; H.-C.S., F.B., Y.-M.S. and V.G.-O., protein purification; H.-C.S. and Y.-M.S., structure determination and biochemical experiments; J.B. and Y.-G.K., X-ray data collection and structure determination; F.B., H.-C.S., S.G. and B.-H.O. conception of experiments and preparation of the manuscript.

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Correspondence to Byung-Ha Oh or Stephan Gruber.

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Bürmann, F., Shin, H., Basquin, J. et al. An asymmetric SMC–kleisin bridge in prokaryotic condensin. Nat Struct Mol Biol 20, 371–379 (2013).

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