A biological motor responsible for folding DNA actually grips tighter when you try to pull it off.
Most molecular bonds are like Velcro and will snap apart if they are subjected to enough mechanical force. The condensin motor, which organizes the genome, uses rare catch bonds that do the exact opposite. As external tension increases, the lifetime of the motor’s grip on the DNA strand actually lengthens. This bizarre physical property allows the motor to stay attached and continue its work even when the genome is under heavy stress. Understanding this mechanism explains how our cells manage to keep our genetic code organized during the violent process of cell division.
Loop Extrusion Reversal by Condensin Motor is Mediated by Catch Bonds
arXiv · 2605.04482
Structural Maintenance Complexes (SMC) are energy consuming motors that are important in folding the genome by loop extrusion (LE) in all stages of the cell cycle. Single molecule magnetic tweezer pulling experiments have revealed that condensin, a member of the SMC family involved in mitosis, takes occasional backward steps, thus coughing up the gains in the length of the extruded loop. To reveal the mechanism of the forward and backward steps simultaneously, we developed a theory using the sto