Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - CondStruct (Structural basis for the coordination of chromosome architecture by condensin complexes)

Teaser

The correct function of all genomes depends on their precise spatial and temporal organization in the cell. How the large-scale topology of chromatin fibers inside the eukaryotic nucleus is controlled and how this architecture changes during cell divisions to give rise to...

Summary

The correct function of all genomes depends on their precise spatial and temporal organization in the cell. How the large-scale topology of chromatin fibers inside the eukaryotic nucleus is controlled and how this architecture changes during cell divisions to give rise to rod-shaped mitotic chromosomes have remained central unsolved questions of the life sciences. Errors in the three-dimensional positioning of genes during interphase can result in the misregulation of gene expression or unrestrained recombination events, while failure to condense chromosomes into compact entities during mitosis or meiosis can result in chromosome breakage, rearrangements, or aneuploidies. All these events are hallmarks of various human disease conditions, including cancer, genetic disorders or infertility.

Understanding the principles that maintain the integrity of genomes during health and how these change during disease is hence of utmost importance for society. During the recent years, multi-subunit protein complexes of the Structural Maintenance of Chromosomes (SMC) protein family have emerged as the central regulators of chromosome organization. The key objective of the research funded by this ERC Grant is to elucidate the molecular mechanisms of the eukaryotic condensin complex to understand how SMC protein complexes affect and preserve the architecture of eukaryotic genomes.

Work performed

During the first reporting period, we have established expression and purification protocols for the five subunits of condensin complexes from different species. Using these protocols, we have been able to obtain highly pure condensin holocomplexes in amounts sufficient for functional and structural studies. In a collaboration with the groups of Prof. Eric Greene (Columbia University, New York) and Prof. Cees Dekker (Technical University of Delft), we demonstrated that these complexes function as DNA motors that unidirectionally translocate over several kilobase pairs of DNA fueled by the energy of ATP hydrolysis (Terakawa et al., Science 2017). We furthermore showed that this DNA motor activity provides the basis for the processive extrusion of DNA into large loop structures (Ganji et al., Science 2018), which explains how condensin compacts DNA (Eeftens et al., EMBO J 2017). Finally, we revealed at near-atomic resolution how condensin stably binds DNA using a unique ‘safety-belt’ mechanism (Kschonsak et al., Cell 2018), which explains how the complex can extrude DNA loops unidirectionally.

Final results

The discovery of condensin’s DNA motor and loop extrusion activities provided the first evidence for the proposal that SMC protein complexes can actively fold eukaryotic genomes and, as such, revolutionized the current understanding of genome organization. The key question that arises from this discovery is how condensin can convert the chemical energy from ATP hydrolysis into physical movement along the DNA double helix. The second part of the research program will therefore focus on solving the detailed mechanism behind the condensin DNA motor activity. Towards this goal, we anticipate that we will solve the structure of the condensin holocomplex using integrative structural biology methods (x-ray protein crystallography, nuclear magnetic resonance spectroscopy, cryo-electron microscopy, protein cross-linking) before the conclusion of the project.

Website & more info

More info: http://www.haering.embl.de.