Powered by
Website address:
https://www.gesundheitsindustriebw.de/en/article/news/martin-beck-and-the-nuclear-poreatlas/
Martin Beck and the nuclear pore atlas
Dr. Martin Beck from the European Molecular Biology Laboratory in Heidelberg was awarded
an ERC Starting Grant for his project “Atlas of Cell-Type Specific Nuclear Pore Complex
Structures”. The combination of cryo-electron microscope tomography, proteomics and
biochemical methods will enable the creation of a high-resolution three-dimensional image
of the nuclear pore complex.
Three-dimensional reconstruction of a nuclear pore, seen from the cell nucleus. © MPG
The double membrane, which separates the chromosome-containing nuclear space
(karyoplasm or nucleoplasm) from the cytoplasm, is a fundamental characteristic of eukaryotic
cells. In the majority of cells, the nuclear membrane is connected to the endoplasmic
reticulum, but differs from the latter and all other membrane systems due to the presence of
nuclear pores that enable the controlled exchange of molecules (in particular RNAs and
proteins) between the nucleo- and the cytoplasm.
Since Werner Franke (then at the University of Freiburg, later at the German Cancer Research
Center) carried out electron microscope investigations of isolated nuclear membranes in the
late-1960s, it has been known that the nuclear pores are not just simple holes in the
membrane, but complex three-dimensional structures consisting of numerous components.
Many researchers over the last twenty years, including the Nobel Laureate Günter Blobel and
the biochemist Ed Hurt from Heidelberg (see BIOPRO article entitled "In vitro modeling of the
nuclear pore complex of a thermophilic fungus"), have studied the structure and function of
nuclear pores in great detail. It is now known that the nuclear pore complex is not just one of
the biggest supramolecular cell structures consisting of at least 30 different proteins
(nucleoporins), but that it is also a dynamic machine associated with many other components
that enable the regulated and controlled transport of macromolecules between the nuclear
1
space and the cytoplasm.
It is also assumed that the nuclear pore complex plays a role in the segregation of
chromosomes prior to cell division (mitosis). While the organisation of the nuclear pore
complex seems to have remained highly conserved throughout evolution, some of the species
investigated display characteristic differences in terms of composition and function. In higher
organisms, the nuclear pore complex (NPC) disintegrates during mitosis and the dissolution of
the nuclear membrane and reassembles in the daughter cells after cell division. In many lower
eukaryotes such as yeasts, for example, the nuclear membrane and the nuclear pores remain
intact when the cells divide.
Cryo-electron tomography
Dr. Martin Beck © EMBL
Dr. Martin Beck, head of a group of researchers at the European Molecular Biology Laboratory
in Heidelberg, has made a name for himself with his achievements in elucidating the structure
and function of molecular machines such as NPCs. He used innovative proteomics methods
and cryo-electron microscopy for his examinations. In September 2012, the European Research
Council (ERC) announced that it had selected Beck as one of the young European scientists
who would receive a renowned ERC Starting Grant. The ERC gave Beck the grant for a project
aimed at developing an atlas of the cell-type specific structures of the nuclear pore complex.
Beck did his doctoral thesis in the Molecular Structural Biology department led by Professor Dr.
Wolfgang Baumeister at the Max Planck Institute of Biochemistry in Martinsried, and at this
stage he was already focusing on the structure of nuclear pores. Back then, Baumeister and
his team were, and still are, worldwide leaders in the development of cryo-electron
tomography (CET), a unique technology that allows the three-dimensional representation of
macromolecular complexes in their native environment. A series of electron microscope images
of snap-frozen cells and cell components is produced in a similar way to computed tomography
and assembled into a 3D image by a computer. The sample can be rotated in order to obtain
images from different angles. The procedure has the potential to close the gap between the
molecular and cellular dimensions in the field of structural biology. Using statistical analyses of
around 250 NPCs recorded from different angles, Beck and his colleagues were able to
reconstruct the three-dimensional structure of the pore complex and assign it to different
functional states. They have shown that the structures of high electron density of the pore
channels are not integral NPC components; instead they have been found to be cargo
molecules, i.e. particles that are transported around.
2
From structure to function
Structure of the nuclear pore complex showing a “nuclear basket” on the inner membrane – CET analyses carried
out by M. Beck. © EMBL
After completing his doctorate, Martin Beck joined the laboratory of Professor Ruedi Aebersold
at the Swiss Federal Institute of Technology in Zurich in 2006. Ruedi Aebersold is a pioneer of
proteome research. New developments in the field of proteomics excellently complement CET
investigations in the acquisition of information about the function of NCPs and the
development of high-resolution models of these molecular machines. Mass spectrometry can
be used to investigate complex protein mixtures and to obtain quantitative information about
the proportions of the protein components in the complexes. This usually involves using
specifically labelled reference peptides. The spatial orientation of proteins can be determined
by carefully linking the individual components with each other. Beck has been the head of the
research group “Structure and Function of Large Macromolecular Assemblies” at the European
Molecular Biology Laboratory in Heidelberg since 2010. The team not only investigates NPCs,
but also other macromolecular complexes consisting of many different components, including
proteasomes. In order to do this, the team use CET and proteomics methods which Beck first
learned to use in the laboratories of Baumeister and Aebersold and which he has developed
further.
In Martinsried, Beck investigated the nuclear pores of nuclei isolated from Dictyostelium
discoideum, a fungus Professor Günther Gerisch helped to make the model organsim in the
field of cell biology. Information about the NPCs of a number of organisms of different
evolutionary stages is now available, including unicellular yeasts, clawed frogs (Xenopus) and
humans. The structure of human NPCs is very similar to that of Xenopus NPCs whereas the
NPCs of lower eukaryotes like Dictyostelium differ considerably. Characteristic differences have
also been found between certain cell types with different functions within a single species. The
ERC Starting Grant will now enable Beck and his team to systematically investigate cell-type
specific NPC structures. The researchers hope that they will be able to represent the structures
in action and gain new insights into how the selective energy-dependent transport of large
macromolecules through the pore channel works. In addition, they also hope to elucidate the
processes that enable the individual components of the nuclear pore complex to assemble into
a ‘gigantic’ machinery with a molecular weight of more than 100 million Da and disintegrate
again when the cell divides and the nuclear membrane dissolves.
3
Article
08-Oct-2012
EJ (02.10.2012)
BioRN
© BIOPRO Baden-Württemberg GmbH
The article is part of the following dossiers
The human proteome – the next major goal
4