Harnessing Cellular Machines for Humans
The cell is loaded with molecular machines, so why reinvent the wheel? or the whole truck? Martin G. L. van den Heuvel and Cees Dekker wrote in Science that engineers ought to put the existing technology to work.1
The biological cell is equipped with a variety of molecular machines that perform complex mechanical tasks such as cell division or intracellular transport. One can envision employing these biological motors in artificial environments. We review the progress that has been made in using motor proteins for powering or manipulating nanoscale components. In particular, kinesin and myosin biomotors that move along linear biofilaments have been widely explored as active components. Currently realized applications are merely proof-of-principle demonstrations. Yet, the sheer availability of an entire ready-to-use toolbox of nanosized biological motors is a great opportunity that calls for exploration.
It’s time to put these ready and willing workhorses to work. Their illustration shows diagrams of ATP synthase and a bacterial flagellum, kinesin, dynein, myosin and RNA polymerase. Of the flagellum, they said, “This powerful motor, assembled from more than 20 different proteins, is driven by an inward proton flux that is converted by several torque-generating stators into a rotary motion of the cylindrical rings and central shaft.”
They reviewed the various motors and experiments to date to harness and control them. Some day we might use cellular motors to sort, assemble, concentrate or manufacture materials on demand. Or, we might try to copy them from scratch with our own building blocks. But why do that? “The small size and force-exerting capabilities of motor proteins and the range of opportunities for specific engineering give them unique advantages over current human-made motors,” they said. The sky is the limit; the field seems limited only by our own imaginations. “Upon studying and using biomotors, we will gather a lot of knowledge that is of interest to biology, material science, and chemistry, and it is reasonable to expect spin-offs for medicine, sensors, electronics, or engineering,” they concluded. “The exploration of biomotors in technology will thus remain an interdisciplinary playground for many years to come.”
Oh, one other thing. They did make a quick comment about where these machines came from. Here is paragraph two of their article:
A huge amount of biological research in recent decades has spurred the realization that the living cell can be viewed as a miniature factory that contains a large collection of dedicated protein machines (1)2. Consider the complicated tasks that a single cell can perform: It can create a full copy of itself in less than an hour; it can proofread and repair errors in its own DNA, sense its environment and respond to it, change its shape and morphology, and obtain energy from photosynthesis or metabolism, using principles that are similar to solar cells or batteries. All this functionality derives from thousands of sophisticated proteins, optimized by billions of years of evolution. At the moment, we can only dream of constructing machines of similar size that possess just a fraction of the functionality of these natural wonders.
While we’re on the subject, let’s look at a cellular device that recently got more praise: the cilium. This little rod-like projection on most cells is doing more work than previously thought. “Appreciation is now growing for primary cilia,” said Christenson and Ott in Science,3 primary cilia being “the nonmotile counterparts, present as a single copy on the surface of most cell types in our body.”
If primary cilia don’t beat and wave like the moving kind, what do they do? Well, for one thing, “they function as unique antenna-like structures, probing the extracellular environment for molecules that are recognized by the receptors they bear. This sensory function allows primary cilia to coordinate numerous intercellular signaling pathways that regulate growth, survival, and differentiation of cells during embryonic development and maintenance of healthy tissues.” New research shows that a suite of molecules move in a coordinated fashion in and out of the cilium, creating a powerful switch by which cells can turn on and off a set of signaling pathways. That’s pretty cool for an complex antenna previously thought to be nothing more than a little bitty hair on a tiny cell.4
1Martin G. L. van den Heuvel and Cees Dekker, “Motor Proteins at Work for Nanotechnology,” Nature 20 July 2007: Vol. 317. no. 5836, pp. 333-336, DOI: 10.1126/science.1139570.
2This reference was to Bruce Alberts’ 1998 paper that made a similar statement, calling the study of molecular machines the “biology of the future” (see 01/09/2002).
3Søren Tvorup Christensen and Carolyn Marie Ott, “Cell Signaling: A Ciliary Signaling Switch,” Science, 20 July 2007: Vol. 317. no. 5836, pp. 330-331, DOI: 10.1126/science.1146180.
4The ones that move are way cool: see 12/19/2005, 03/12/2001.
So, “thousands of sophisticated proteins, optimized by billions of years of evolution.” Gimme a BREAK!