Proteins hoist the anchor
How switch proteins are extracted from the membrane
Researchers from the Ruhr-Universität Bochum (RUB) and from the MPI Dortmund have for the first time successfully reproduced the recycling process of proteins regulating cellular transport in a biophysical experiment. In doing so, they traced in detail the way the central switch protein Rab is being extracted from the lipid membrane. The team of PD Dr Carsten Kötting, Prof Dr Klaus Gerwert (Department of Biophysics, RUB) and Prof Dr Roger S. Goody (Max Planck Institute for Molecular Physiology, Dortmund) has published the spectroscopic and dynamic data in the PNAS journal's Online Early Edition. "Until now, this protein's interactions have only ever been studied in a solution – i.e. without a lipid membrane. The step into the protein's natural environment opens up entirely new possibilities," says Carsten Kötting. This is because many disease-relevant protein interactions within a cell take place on a membrane.
The Rab protein (grey and magenta) with bound GDP (multi-coloured) sits on a membrane surface. As the infrared ray is reflected from the surface, the processes that take place on the membrane can be studied. The GDI, represented by the hand, seizes the Rab protein and extracts it from the membrane. The timeline of the infrared spectra (top centre) is resolved in the spectrometer (top right).
Konstantin Gavriljuk, RUB
From solution to membrane
Unlike Ras proteins that regulate cell growth, Rab GTPases control the traffic between different cell sections. Just like Ras proteins, Rab GTPases (also called Rab proteins) act as switches. Turned "on", the high-energy GTP molecule is bound; turned "off", the lower-energy GDP molecule is bound. The switch protein Rab does not simply swim through the cell with the trafficked load it is carrying; rather, it is fixed within the membrane by means of lipid anchors. After the trafficking stage has been successfully completed, Rab is extracted from the membrane and recycled. This process has never yet been simulated in a biophysical experiment. The Bochum-Dortmund team has succeeded in manufacturing the Rab protein with the membrane anchor in its active form in large quantities, to bind it to an artificial lipid membrane and to investigate the process of extracting the switch protein from the membrane in a spectrometer.
Seize and pull hard
For this purpose, biophysicists used the method of ATR infrared spectroscopy, which enabled them to visualise processes on surfaces such as lipid membranes. They paid particular attention to the GDI protein that binds the Rab protein and its lipid anchor. The question was whether Rab dissociates spontaneously from the membrane and is seized by GDI or whether GDI plays an active part in the Rab recycling process. With ATR spectroscopy, the team was for the first time able to differentiate between these two processes and demonstrate the GDI protein's active role. "We observed that GDI approaches the membrane and seizes the Rab protein then and there," explains Konstantin Gavriljuk. "Thus, Rab is extracted from the membrane by GDI much more quickly than it would have otherwise dissociated."
Legionella affect cellular trafficking processes
Rab GTPases and their interaction partners have an impact on certain diseases, for example some forms of mental disabilities and legionnaire's disease. The agents causing legionnaire's disease, namely legionella, attack Rab proteins and modify them chemically, thus affecting cellular trafficking processes; they are thus able to reproduce in human cells. The experiments have shown that the chemical modification caused by legionella inhibits the process of Rab extraction from the membrane by GDI. "We have now gained a better understanding of where legionella attack cells and of the consequences thereof," says Carsten Kötting.
Original publication
Other news from the department science
These products might interest you
Hydrosart® Ultrafilter by Sartorius
Efficient ultrafiltration for biotech and pharma
Maximum flow rates and minimum protein loss with Hydrosart® membranes
Hydrosart® Microfilter by Sartorius
Hydrophilic microfilters for bioprocesses
Minimal protein adsorption and high flow rates
Sartobind® Rapid A by Sartorius
Efficient chromatography with disposable membranes
Increase productivity and reduce costs with fast cycle times
Sartopore® Platinum by Sartorius
Efficient filtration with minimal protein adsorption
Reduces rinsing volume by 95 % and offers 1 m² filtration area per 10"
Polyethersulfone Ultrafilter by Sartorius
Reliable filtration with PESU membranes
Perfect for biotechnology and pharmaceuticals, withstands sterilisation and high temperatures
Polyethersulfone Microfilter by Sartorius
Biotechnological filtration made easy
Highly stable 0.1 µm PESU membranes for maximum efficiency
Get the life science industry in your inbox
From now on, don't miss a thing: Our newsletter for biotechnology, pharma and life sciences brings you up to date every Tuesday and Thursday. The latest industry news, product highlights and innovations - compact and easy to understand in your inbox. Researched by us so you don't have to.
Most read news
More news from our other portals
See the theme worlds for related content
Topic World Spectroscopy
Investigation with spectroscopy gives us unique insights into the composition and structure of materials. From UV-Vis spectroscopy to infrared and Raman spectroscopy to fluorescence and atomic absorption spectroscopy, spectroscopy offers us a wide range of analytical techniques to precisely characterize substances. Immerse yourself in the fascinating world of spectroscopy!
Topic World Spectroscopy
Investigation with spectroscopy gives us unique insights into the composition and structure of materials. From UV-Vis spectroscopy to infrared and Raman spectroscopy to fluorescence and atomic absorption spectroscopy, spectroscopy offers us a wide range of analytical techniques to precisely characterize substances. Immerse yourself in the fascinating world of spectroscopy!
