New research into the activity of a key "motor" protein suggests that a unique form of random motion powered by thermal energy may play a vital role in moving enzymes and other chemicals inside cells. Beyond providing a better understanding of sub-cellular functions, the National Science Foundation-sponsored work may offer a new mechanism for generating motion in future nanometer-scale machines.
Within the cells of the body, kinesin proteins work like "cellular tow trucks" to pull tiny sacks of chemicals along pathways known as microtubules. The accepted explanation for this motion is that the kinesins use their two leg-like "heads" to walk along the microtubule paths in a deliberate way, fueled by the energy molecule adenosine triphosphate (ATP).
But in a paper published in May issue of the journal Physical Review E, Georgia Institute of Technology physicist Ronald Fox argues that what appears to be a walk along the microtubule is really random motion cleverly constrained by chemical switching carried out by ATP.
"These are certainly not motors in the sense of burning a fuel and having a concerted effort in a one-directional way," said Fox. "If you could see them, their walk would appear to be more like a drunken sailor than a concerted motion."
Composed of fibrous proteins, the microtubules include sites approximately 8 nanometers apart where kinesin heads can bind chemically. To move along this pathway, Fox argues that the kinesins use "rectified Brownian motion" in the following steps: