Single-molecule mechanics of eukaryotic and bacterial SMC complexes

Structural Maintenance of Chromosomes (SMC) complexes are conserved molecular machines that help organize genomes in organisms ranging from bacteria to humans. They perform two essential tasks: they establish DNA-DNA interactions and extrude DNA loops, thereby shaping chromosome architecture and supporting faithful chromosome segregation. In this talk, I will discuss recent single-molecule studies from our group that reveal how these machines work under force. Using optical tweezers combined with fluorescence microscopy, we directly measure how strongly individual SMC complexes interact with DNA while visualizing their activity. We find that cohesin and condensin can form highly stable DNA connections capable of resisting the forces generated during cell division. By contrast, cohesin-mediated loop extrusion depends on much weaker and more dynamic DNA interactions, allowing loops to be readily remodelled. Comparisons with bacterial SMC complexes show that these machines can be stronger and more efficient loop extruders than their eukaryotic counterparts. Together, these findings suggest that SMC complexes have evolved different mechanical properties to match their specific roles in chromosome folding, maintenance, and segregation.