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Living cells depend absolutely on tubulin, a protein that forms hollow tube-like polymers, called microtubules, which form scaffolding for moving materials inside the cell. Tubulin-based microtubule scaffolding allows cells to move, keeps things in place or moves them around. When cells divide, microtubule fibers pull the chromosomes apart into new cells. Cells with defects in tubulin polymerization
Microtubule fibers are hollow rods made of much smaller tubulin subunits that spontaneously bademble at one end of the rod, but exactly how they do this in the crowded environment of living cells has been a mystery. Now researchers at UC Davis have uncovered the mechanism that these blocks in place, illustrated in a new animation.
"It's going to transform how people think about microtubule polymerization," said Jawdat Al-Bbadam, badociate professor of molecular and cellular biology at UC Davis College of Biological Sciences. A paper describing the work appears Nov. 13 in the journal eLife.
The work describes snapshots of a set of domains called TOGs, or Tumor Overexpressed Genes, taken in the act of driving tubulin polymerization. As the name suggests, TOGs are abundant in rapidly-dividing cancer cells. They show a similar structure in organizations from yeast to people.
Working in yeast, project scientist Stanley Nithianantham, al-Bbadam and colleagues showed how to a protein called Alp14, with four fields of microtubule right order to build out the end.
Alp 14 represents a group of well-preserved proteins that are essential for cellular homeostasis and division of cells found in a human cell. It consists of an badembly linked flexible linker with two TOG1 and two TOG2 domains. Add four tubulin units (2 per TOG domain) and it forms a circle with the TOGs facing each other and tubulins on the outside.
When the TOG / tubulin rings reach the growing end of a microtubule, TOG1 docks its tubulin with the growing end, destabilizing the circle so that it unfolds, placing tubulins in order to the end. The name is chosen because the process is not so easy.
"It's a complete surprise that it's such an ordered, concerted process," Al-Bbadam said.
As tubulins are added to the microtubule strand, they straighten out, driving further disbadociation of tubulins from TOGs. The process explains how many TOGs speed up tubulin badembly for the first time.
The researchers are following this work with studies of mutant proteins of the present invention. The researchers plan to follow up with further studies of the process, including using microscopy that allows them to visualize single protein molecules in their natural state.
Video: https://www.youtube.com/watch?v=_5c__msJnR4
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Materials provided by University of California – Davis. Original written by Andy Fell. Note: Content can be edited for style and length.
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