Abstract
SummaryCondensin protein complexes coordinate the formation of mitotic chromosomes and thereby ensure the successful segregation of replicated genomes. Insights into how condensin complexes bind to chromosomes and alter their topology are essential for understanding the molecular principles behind the large-scale chromatin rearrangements that take place during cell divisions. Here, we identify a direct DNA-binding site in the eukaryotic condensin complex, which is formed by its Ycg1Cnd3 HEAT-repeat and Brn1Cnd2 kleisin subunits. DNA co-crystal structures reveal a conserved, positively charged groove that accommodates the DNA double helix. A peptide loop of the kleisin subunit encircles the bound DNA and, like a safety belt, prevents its dissociation. Firm closure of the kleisin loop around DNA is essential for the association of condensin complexes with chromosomes and their DNA-stimulated ATPase activity. Our data suggest a sophisticated molecular basis for anchoring condensin complexes to chromosomes that enables the formation of large-sized chromatin loops.
Highlights
In preparation for cell divisions, eukaryotic chromosomes undergo large-scale conformational changes to form rodshaped structures that enable their successful segregation into the daughter cells (Hirano et al, 1997; Kschonsak and Haering, 2015)
Condensin protein complexes coordinate the formation of mitotic chromosomes and thereby ensure the successful segregation of replicated genomes
Insights into how condensin complexes bind to chromosomes and alter their topology are essential for understanding the molecular principles behind the large-scale chromatin rearrangements that take place during cell divisions
Summary
In preparation for cell divisions, eukaryotic chromosomes undergo large-scale conformational changes to form rodshaped structures that enable their successful segregation into the daughter cells (Hirano et al, 1997; Kschonsak and Haering, 2015). Multisubunit protein complexes named condensins have been recognized as the major molecular machines that coordinate these changes in genome architecture (Houlard et al, 2015; Uhlmann, 2016). Like other members of the structural maintenance of chromosomes (SMC) family of protein complexes, condensins are characterized by a large, ring-shaped architecture (Anderson et al., 2002; Onn et al, 2007). The condensin ring is formed by heterodimerization of its Smc and Smc subunits via globular ‘‘hinge’’ domains, which are located at one end of 40-nm-long intramolecular antiparallel coiled coils, and the connection of ATP-binding cassette (ABC)-transporter-like ATPase domains at the other end of the coils by the Brn1Cnd, NCAPH/H2 kleisin subunit (Figure 1A). The central region of the kleisin recruits to the condensin ring the Ycs4Cnd, NCAPD2/D3 and Ycg1Cnd, NCAPG/G2 subunits, which contain tandem repeats of amphipathic a helices referred to as HEAT (huntingtin, elongation factor 3, protein phosphatase 2A, Tor kinase) motifs (Andrade and Bork, 1995; Neuwald and Hirano, 2000)
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