Scientists find a brake that acts when cellular motors run too far

September 5, 2011, Wageningen University
Two paired microtubules in a cell (yellow & green) glide along each other. Thanks to the braking effect of the so-called Ase1 protein (the blue molecules between the two microtubules, called Ase1) their gliding speed diminishes when the overlap between the two microtubules decreases. Thanks to that, the microtubules will not lose hold with each other.

( -- An international team of scientists has shown how microtubules are interconnected into large networks. Like the poles of a tent, microtubules give shape to cells. By sliding microtubules along each other cells self-organize networks and relay forces that move chromosomes around during cell division. The team unravelled a mechanism that can stop the process of two microtubules sliding along each other before the two microtubules will lose their contact.

The research team harboured scientists from the Max Planck Institute of Molecular Cell Biology and Genetics in Germany and Wageningen University in The Netherlands. Independently the groups had previously characterized a motor protein that connects two microtubules whilst walking along it and a more passive connector that acts pretty much like molasses between microtubules. What would happen if both proteins were simultaneously present like in ?

To answer this question postdoctoral researchers Marcus Braun, Zdenek Lansky, and Gero Fink purified all necessary proteins from cells and studied precisely how two microtubules slide along each other in the presence of both components. Marcel Janson, professor of Plant Cell Biology at Wageningen University: “One would think that the sliding velocity of microtubules is set by the ratio of supplied motors and molasses. That was indeed the case when microtubules were happily sliding along one another. However, the system unexpectedly changed the ratio in favour of molasses when the microtubules started to slide apart. So, the resulting microtubule driving force is not constant at all, but changes over time. As a result, microtubules do not separate from each other but stay connected during extended amounts of time.”

An explanation for the phenomenon was found by implementing observations on single molasses-proteins into a quantitative model of microtubule sliding. The binding of individual GFP-tagged proteins to microtubules could be observed using advanced fluorescence microscopy. In between sliding microtubules, the proteins would skid slowly towards the ends of microtubules but would not let go of them. As a consequence, the molasses was compacted when microtubules were sliding apart, explaining the slowdown in sliding.

Stefan Diez group leader at Max Planck and professor at the B CUBE – Center for Molecular Bioengineering at Technische Universität Dresden: “By studying the forces that act between microtubule, we now understand a crucial step in the self-organisation of microtubule networks. We show that microtubules can move along each other to construct the network whilst their ends can stay connected to stabilize the network. In cells, the overlapping part of the is positioned in the middle of the cell, exactly on the spot where the flock together at the beginning of cell division.”

Explore further: One-dimensional Diffusion Accelerates Molecular Motors

More information: M. Braun, Z. Lansky, G. Fink, F. Ruhnow, S. Diez, M. Janson, “Adaptive braking by Ase1 prevents overlapping microtubules from sliding completely apart”, Nat. Cell Biol., online published, doi: 10.1038/ncb2323

Related Stories

One-dimensional Diffusion Accelerates Molecular Motors

May 12, 2006

Max Planck scientists have identified a new strategy which motor proteins use to move. The research was carried out by Prof. Jonathon Howard and Stefan Diez at the Max Planck Institute of Molecular Cell Biology and Genetics ...

Surprising origin of cell's internal highways

June 20, 2007

Scientists have long thought that microtubules, part of the microscopic scaffolding that the cell uses to move things around in order to hold its shape and divide, originated from a tiny structure near the nucleus, called ...

The downside of microtubule stability

June 15, 2009

Stalled microtubules might be responsible for some cases of the neurological disorder Charcot-Marie-Tooth (CMT) disease, Tanabe and Takei report in the Journal of Cell Biology . A mutant protein makes the microtubules too ...

Roadworks on the motorways of the cell

December 28, 2006

A cell is a busy place. In a permanent rush hour, molecules are transported along a dynamic motorway system made up of filaments called microtubules. Microtubules constantly grow and shrink and are rapidly assembled wherever ...

Recommended for you

Cells lacking nuclei struggle to move in 3-D environments

January 20, 2018

University of North Carolina Lineberger Comprehensive Cancer Center researchers have revealed new details of how the physical properties of the nucleus influence how cells can move around different environments - such as ...

Microbial communities demonstrate high turnover

January 19, 2018

When Mark Twain famously said "If you don't like the weather in New England, just wait a few minutes," he probably didn't anticipate MIT researchers would apply his remark to their microbial research. But a new study does ...


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (4) Sep 05, 2011
So the evergreen question is: Just how did this evolve? OR NOT?
When will people give up on the magical, mythical, mystical evolutionary force/god that is capable of all kinds of wonderous, most incredible nanotechnology that even the most intelligent of human beings find hard to emulate? WHen?
not rated yet Sep 05, 2011
Even the solely physical droplets are capable of locomotion and they're able to seek the "food" through maze.

not rated yet Sep 05, 2011
People will give up on the magical, mythical, mystical, evolutionary force/god that is capable of all kinds of wondrous, most incredible nanotechnology when:

You provide the same motivation that inspires the same effort to emulate all things, regardless of intelligence or degree of difficulty to do so. :)
not rated yet Sep 05, 2011
Thks for the link. Most impressive.
All taxes with all gradients. Yes. Magical, mystical, evolutionary, all-capable, wondrous, and most incredible.
Without intelligence and easy to emulate.
A good starting point.
For kevinrtrs.
1 / 5 (1) Sep 06, 2011
So the evergreen question is: Just how did this evolve? OR NOT?

I'm not an expert on this topic but it seems to me that if this mechanism gives cells their shape then cells would survive better because of it...

When will people give up on the... blah blah blah

When a better alternative is presented.

5 / 5 (1) Sep 07, 2011
Kevin, read the article. Let me help: "An explanation for the phenomenon was found by implementing observations on single molasses-proteins into a quantitative model of microtubule sliding."

The only real "evergreen question" is "When will kevinrtrs give up on his magical god that creates everything without evolution?"

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.