A dynamic gel made of DNA that mechanically responds to stimuli in much the same way that cells do has been created by UC Santa Barbara scientists Omar Saleh and Deborah Fygenson have created. 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. The project has potential applications in smart materials, artificial muscle, understanding cytoskeletal mechanics, research into nonequilibrium physics, and DNA nanotechnology.
“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,” said Saleh, associate professor of materials, affiliated with UCSB’s Biomolecular Science and Engineering program.
“DNA gives you a lot more design control,” said Fygenson, associate professor of physics and also affiliated with UCSB’s BMSE program. “This system is exciting because we can build nanoscale 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.
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.
“The development of active gels represents a water-shed event for the broader materials community,” commented Craig Hawker, director of the Materials Research Laboratory at UCSB: an NSF MRSEC, which provided seed money for their research. “By exploiting cellular building blocks, it offers unique design parameters when compared to existing gel systems that can be used in a wide range of both established biomedical applications as well as totally new applications.”
Having created a gel that can replicate contractions, Saleh and Fygenson are now looking to refine their technique and enable distinct movements, such as twisting and crawling, or using other motor proteins that would allow the gel to mimic other cell behaviors, such as shape-shifting and dividing.
“Biology provides a wide range of motors that we have only begun to explore,” Saleh said.
The image at the top of the page shows DNA gel composed of stiff DNA nanotubes connected to each other via long, flexible DNA linkers. A motor protein, FtsK50C, binds to special sites on the linkers. When ATP, a biochemical fuel, is allowed to permeate the gel, the motor molecules reel in the linkers to which they are bound, drawing nanotubes together, and stiffening the gel.
For more information: Olivier J. N. Bertrand, Deborah Kuchnir Fygenson, and Omar A. Saleh, Active, motor-driven mechanics in a DNA gel, PNAS, 2012, DOI: 10.1073/pnas.1208732109
Image credit: Peter Allen/UCSB
Source: The Daily Galaxy via UC Santa Barbara