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Nanoscale Motors

Biophysicist Carlos Bustamante marvels at the ways in which our ability to observe single molecules has changed our understanding of biology. Until recently, proteins were thought of simply as catalysts that make reactions in living things happen faster. “In the last 20 years,” Bustamante says, “biologists have come to realize that proteins actually seem more like molecular machines.” In fact, it turns out that proteins and other biological molecules are some of the most efficient machines on earth. ENSI researchers are striving to understand the source of that efficiency, and apply it to new types of motors.

"How we can make this biological machine do     something besides what it normally does?"  
- Carlos Bustamante 

Bustamante, Professor of Chemistry, Physics, and Molecular and Cell Biology and UC Berkeley, has spent years observing the ways proteins like motors, turning chemical energy into mechanical energy that can do work. In some ways, proteins are similar to motors we’re familiar with. In a car engine, for instance, a spark plug sets off a reaction in which the chemical bonds in gasoline and air are broken. The energy released by the formation of new bonds and new chemical species pushes the motor’s pistons. That motion of the piston is eventually translated into the work that moves the car forward.

To study the motor-like properties of proteins, Bustamante observes single molecules using an instrument called optical tweezers. Using light, Bustamante can literally grab a single molecular motor and stretch it, as if he were playing tug-of-war. Then he measures the force it generates as it moves on its track.  In doing this, he’s determined that while a cell is using proteins to catalyze reactions, force itself is one of the products of those reactions. Bustamante has also carefully measured the efficiency of these tiny nano-engines.

A double-stranded DNA molecule suspended between optical tweezers. Image: Phys.org

A double-stranded DNA molecule suspended between optical tweezers. Image: Phys.org

Ideally, Bustamante says, we’ll be able tweak these highly complex, highly evolved biological motors so that they can carry out functions beyond those they evolved to do. At the same time, researchers can also apply lessons learned to manmade motors. With that in mind, Bustamante has begun working with UC Berkeley physics professor Alex Zettl, who designs his own nanoscale motors.

Zettl, a specialist in solid state and materials physics, has already created synthetic electric nanomotors that are as small as the biological motors Bustamante is working on, but 1000 times more forceful.  In addition, unlike biomotors, the synthetic motors operate over a very wide range of temperature and environmental conditions, making them useful for widely different applications.  Zettl has also calculated that his nanomotors have a power density more than 10,000 times that of a conventional car motor.  At the moment, his “nanomachine” is typically just a tiny motor than can push other tiny things. He’s inspired, though, by the system that makes muscles contract. That system is comprised of protein molecules, molecular motors that aren’t all that powerful on their own. But putting millions of them together in a muscle fiber, and putting thousands of fibers together, allows these mini motors to do massive amounts of work.

“What if I could put a gang of these little motors in a car?” Zettl proposes. “I could put enough of them together to power my car with an engine that’s about the size of my thumb. That makes a huge difference in terms of efficiency and resource conservation.”

Zettl and Bustamante have talked about making a hybrid motor, which could have great advantages. In our macroscopic world, we have many examples of hybrid motors, such as the diesel-electric locomotives that power trains. At the nanoscale, the challenges are a bit different. “You might have a sophisticated biological system, and you want to be able to use it without going through another complicated biological system,” Zettl says. The trick lies in isolating the biological motor and coupling it with a synthetic motor to make it accessible. “We have to interface the two worlds together.”

Accomplishing that interface won’t be simple, and both researchers say it’s only possible with the kind of opportunities for collaboration that the Kavli’s ENSI institute provides. “We’re all interested in the same kind of thing,” says Zettl. “It used to be that we had different lexicons, a cultural barrier. But now we realize that the science is universal, and different approaches can be complementary.”

Bustamante also appreciates how such collaborations can further understanding. “I can ask, ‘How we can make this biological machine do something besides what is normally does?’ And then I can talk to Alex, and we can put something together.”

“It expands the domain of ideas that we can investigate,” he says. “For me, that’s the really exciting part.”

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