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| Heidelberg, 29 December 2006 |
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| Roadworks on the motorways of the cell |
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In the absence on Mal3p microtubules are unstable and can open at the
seam. The image shows a microtubule with opening seam [bottom left],
seen through the electron microscope. |
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Researchers discover how a protein stabilises microtubules by binding to
their weakest point
Press
Release 29 December 2006 [PDF]
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 a cargo needs to go, but during this transportation
process they need to be kept stable. Researchers from the
European Molecular Biology Laboratory [EMBL] have discovered
for the first time that a protein stabilises microtubules by
binding to their weakest part, the so-called lattice seam. The
study, which appears in this week's issue of the journal Cell, also
suggests that the protein creates a special surface along the seam
that offers an alternative track for transportation.
The basic building blocks of microtubules are proteins called
tubulins. They assemble in a single line to form so-called protofilaments,
of which several combine to build a large tubulin sheet.
Investigating how this sheet folds into the tube-like structures of
microtubules in yeast, researchers have now discovered that a
protein called Mal3p is crucial. Combining molecular techniques
with a unique Electron Microscope setup based at the ETH in
Zürich, they found that Mal3p binds to the seam of the microtubule,
which forms as the two sides of the tubulin sheet fold into
a tube. The protein binds in a single line along the seam, seals the
tube and stabilises it at its weakest point.
"It is the first time that we've found a protein that specifically
binds to the microtubule seam," says Andreas Hoenger, former
group leader at EMBL who has just moved to head a lab at the
University of Colorado. "Until now the function of the seam has
been unknown and it has been largely ignored as an odd and irrelevant
part of the microtubule lattice. Our experiments now reveal
it as a central spot where microtubule stability can be regulated."
Without Mal3p, microtubules are unstable and likely to disassemble,
while in its presence they grow into long filaments. Mal3p
could function as a key regulator of microtubule behaviour.
Controlling its presence allows fast switches between growth and
shrinkage of microtubules, which are essential for rapid and flexible
cellular transport. Mal3p's location along the microtubule
seam is crucial, because here it can confer stability without
obstructing the traffic of motor proteins along the filament. Apart
from its stabilising role, Mal3P could also play a more active role
in transportation.
"Motor proteins move along microtubules through direct interaction
with tubulin. They transport cargo similarly to trucks driving
on motorways," explains Damian Brunner, group leader at
EMBL. "The line of Mal3p along the seam potentially creates an
alternative track on the filament, along which a specialized type of
motor protein could move, just like creating a railway track along
a motorway. This dual system could make transport more diverse
and efficient."
The new insights gained into cellular transport and the stabilisation
of microtubules in yeast might help shed light on how similar
processes work in humans. Mal3p is highly conserved across
species and its human counterpart plays a role in various clinical
conditions, such as colon cancer or neurodegenerative diseases.
Source Article
L. Sandblad, K.E. Busch. P. Tittmann, H. Gross, D. Brunner & A. Hoenger. The Schizosaccharomyces pombe EB1 homolog Mal3p
binds and stabilises the microtubule lattice seam. Cell, 29 December 2006
Press Contact
Anna-Lynn Wegener
Press Officer
EMBL Heidelberg
Tel: +49 +6221 387-8452
Email: wegener@embl.de |
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