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In nerve cells: an energy source nobody knew about.

Maybe this discovery is interesting because it sheds therapeutic light on the dreaded neurodegenerative diseases that killed Woody Guthrie and Lou Gehrig. Or maybe it's fascination with healthy cells, and yet another unsuspected complexity in how they work. What's discovered: a previously unknown energy source in nerve cells. [caption id="attachment_57" align="alignleft" width="408" caption="Kineisin with cargo on microtubules. Photo credit: Vale Laboratories, used by permission."]Kineisin with cargo on microtubules. Photo credit: Vale Laboratories, used by permission.[/caption] It propels the molecular "motors" that drag neurotransmitters from the nucleus where they're made. The "motors" are assemblies of molecules. They walk like clumsy robots, with a staggering gait, dragging a capsule of neurotransmitter "bullets" along microtubule "highways" between nucleus and synapses. They move by flinging their boot-like feet (lavender blobs, in the image) forward, a billionth of a meter at each step. (A superb animation of "motors" in action is XVIVO's "Life of a Cell" (at ~1:15 of playing time)). When the cargo finally arrives at the synapses, neurotransmitters are loaded into compartments at the synapse's interior face, like bullets into a magazine. They are ready to be "fired" across a synapse to signal an adjoining neuron. It's this transport of neurotransmitter "bullets" that failed in Guthrie's and Gehrig's nerve cells. Their synapses had nothing to fire. What powers the flinging that moves those boots? Previously, the answer has been specialized molecules (acronym: ATP) spewed into the cell's fluid interior by mitochondria. The boots, it was thought, powered each step by grabbing a floating ATP and blowing it up like a firecracker. But no. Now it seems that the capsule the motors drag carries its own power source. That source is an enzyme that creates ATP from other molecules inside the cell. The motors don't need mitochondria. Somehow, the enzyme is carried along by the huntingtin protein - which is mutated in Woody Guthrie's disease (Huntington's Chorea), suggesting a link to the disease. Perhaps it's attached to those balloon-like capsules in the image above. So far, nobody knows. Why is this important? A previously unsuspected device by which neurons achieve one of their most important functions. Eventually, perhaps, this understanding will lead to a cure for awful diseases. G. Schiavo and M. Fainzilber, Alternative energy for neuronal motors, 495 Nature 178-179, 14 March 2013.

The views expressed are those of the author and are not necessarily those of Scientific American.

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