"Mechanically Active" DNA Material

Photo: Typical DNA gel used for the study

In this fluorescent micrograph, the
stiff DNA nanotubes are visible as
glowing green and red fibers;

"This is a whole new kind of responsive gel, or what some might call a 'smart' material," said Omar Saleh. "The gel has active mechanical capabilities in that it generates forces independently, leading to changes in elasticity or shape, when fed ATP molecules for energy — much like a living cell."

Their DNA gel, at only 10 microns in width, is roughly the size of a eukaryotic cell, the type of cell of which humans are made. The miniscule gel contains within it stiff DNA nanotubes linked together by longer, flexible DNA strands that serve as the substrate for molecular motors.

"DNA gives you a lot more design control," said Deborah Fygenson. "This system is exciting because we can build nano-scale filaments to specifications." Using DNA design, she said, they can control the stiffness of the nanotubes and the manner and extent of their cross-linking, which will determine how the gel responds to stimuli.

Using a bacterial motor protein called FtsK50C, the scientists can cause the gel to react in the same way cytoskeletons react to the motor protein myosin — by contracting and stiffening. The protein binds to predetermined surfaces on the long linking filaments, and reels them in, shortening them and bringing the stiffer nanotubes closer together. To determine the gel's movement the scientists attached a tiny bead to its surface and measured its position before and after activation with the motor protein.

The breakthrough, said Saleh, is that this gel "quantitatively shows similar active fluctuations and mechanics to cells."

"This new material could provide a means for controllably testing active gel mechanics in a way that will tell us more about how the cytoskeleton works," Saleh said. Like a cell, which consumes adenosine triphosphate (ATP) for energy, the DNA gel's movement runs on ATP, allowing for faster, stronger mechanics than other smart gels based on synthetic polymers.

MEDICA.de; Source: University of California Santa Barbara