New approach solves large molecular puzzles
Friday, 12 July 2013
 |
At
first glance, this may look like the latest view
from a
telescope, but it was taken by looking not
out at
the vastness of space, but into a human
cell.
What could pass for stars or distant galaxies
are
actually gates to the genome that is locked up
inside
the cell's nucleus, as imaged by a super-
resolution
microscope. By combining images of
thousands
of these gates, called nuclear pore
complexes,
scientists at the European Molecular
Biology
Laboratory (EMBL) in Heidelberg,
Germany,
have solved a decade-old controversy
over
how the pieces that form each pore's ring are
arranged. Credit: EMBL/A.Szymborska.
|
In a study published online today in Science, the scientists used super-resolution microscopy to solve a decade-long debate about the structure of the nuclear pore complex, which controls access to the genome by acting as a gate into the cell's nucleus.
Like the bewildered parent staring at the image on the box, scientists knew the gate's overall shape, from electron tomography studies. And thanks to techniques like X-ray crystallography and single particle electron microscopy, they knew that the ring which studs the nucleus' wall and controls what passes in and out is formed by sixteen or thirty-two copies of a Y-shaped building block. They even knew that each Y is formed by nine proteins. But how the Y’s are arranged to form a ring was up for debate.
"When we looked at our images, there was no question: they have to be lying head-to-tail around the hole" says Anna Szymborska, who carried out the work.
To figure out how the Y’s were arranged, the EMBL scientists used fluorescent tags to label a series of points along each of the Y's arms and tail, and analysed them under a super-resolution microscope. By combining images from thousands of nuclear pores, they were able to obtain measurements of where each of those points was, in relation to the pore's centre, with a precision of less than a nanometre – a millionth of a millimetre. The result was a rainbow of rings whose order and spacing meant the Y-shaped molecules in the nuclear pore must lie in an orderly circle around the opening, all with the same arm of the Y pointing toward the pore's centre.
Having resolved this decade-old controversy, the scientists intend to delve deeper into the mysteries of the nuclear pore – determining whether the circle of Y’s is arranged clockwise or anticlockwise, studying it at different stages of assembly, looking at other parts of the pore, and investigating it in three dimensions.
"There's been a lot of interest from other groups, so we'll soon be looking into a number of other molecular puzzles, like the different 'machines' that allow a cell to divide, which are also built from hundreds of pieces," says Jan Ellenberg, who led the work.
The work was carried out in collaboration with John Briggs' group at EMBL, who helped adapt the image averaging algorithms from electron microscopy to super-resolution microscopy, and Volker Cordes at the Max Planck Institute for Biophysical Chemistry in Göttingen, Germany, who provided antibodies and advice.
Contact: Sonia Furtado Neves
Reference:
Nuclear Pore Scaffold Structure Analyzed by Super-Resolution Microscopy and Particle Averaging
Szymborska, A., Marco, A., Daigle, N., Cordes, V.C., Briggs, J.A.G. & Ellenberg, J.
Science Express on 11 July 2013. DOI: 10.1126/science.1240672
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