Article: article from journal or magazin.
An asymmetric SMC-kleisin bridge in prokaryotic condensin.
Nature Structural and Molecular Biology
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.
Adenosine Triphosphatases/chemistry, Adenosine Triphosphatases/metabolism, Bacterial Proteins/chemistry, Bacterial Proteins/genetics, Binding Sites, Cell Cycle Proteins/chemistry, Cell Cycle Proteins/genetics, Cross-Linking Reagents, Crystallography, X-Ray, DNA-Binding Proteins/chemistry, DNA-Binding Proteins/metabolism, Models, Molecular, Multiprotein Complexes/chemistry, Multiprotein Complexes/metabolism, Mutation, Protein Conformation, Protein Multimerization, Protein Structure, Tertiary, Streptococcus pneumoniae/chemistry
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