Using artificial lipid vesicles, biochemists show how membrane proteins transport ammonium.
Do they carry the gas ammonia or the ammonium ion in their luggage? And is transport active or passive?
Biochemists have long speculate on the mechanistic details of the ammonium transport family of proteins (Amt), which include the Rhesus protein factors, known as the mammalian blood group system.
What was previously known is that Amt proteins extend across cellular membranes where they specifically transport the nitrogen into bacteria and plant cells, essential nutrient for their growth and survival. In mammals, Rhesus proteins regulate acid and ion balance in kidney and liver cells.
A team of scientists led by Prof. Dr. Susana Andrade from the Institute of Biochemistry of the University of Freiburg and the Cluster of Excellence BIOSS Centre for Biological Signalling Studies has now determined the transport properties of Amt proteins with great precision on the basis of electrophysiology tests on artificial lipid systems.
The scientists cloned the membrane proteins from an archaea, a microorganisms that lives under extreme temperature conditions and isolate them. In 2005, the Freiburg researchers already threw light on the crystalline three-dimensional structure of a protein of this kind.
Now they have added the protein to a layer of lipid molecules, enabling them to measure the ion currents directly. The team discovered that a positive charge travels through the membrane: The membrane proteins do not transport the gas ammonia NH3 but rather the ammonium ion NH4+. The researchers published their findings in the journal Proceedings of the National Academy of Sciences of the USA.
“The results can, in a large part, be transferred to the Rhesus proteins from mammals,” says Andrade as Amt proteins bear a close resemblance to the Rhesus proteins found in humans. They are produced in the blood, in the kidney, and in the liver, where they regulate the intake of ammonium and thus the body’s pH.
The researchers tested three Amt proteins that are present in the bacteria and also determined the speed with which they allow ammonium to pass through the membrane. “In the future, we want to modify individual components of the transporter to improve our understanding of the exact molecular details involved” explains Andrade.
The scientific debate on Amt/Rh proteins stems from the difficulty of distinguishing between ammonia and ammonium in measurements, as the two molecules are transformed into each other in a continuous state of balance with protons. “Our in vitro method gives us a level of precision that finally allows us to draw valid conclusions concerning the transport process,” stresses the researcher.
Tobias Wacker, Juan J. Garcia-Celma, Philipp Lewe, and Susana L. A. Andrade, Direct observation of electrogenic NH4+ transport in ammonium transport (Amt) proteins, PNAS 2014; published ahead of print June 23, 2014, doi:10.1073/pnas.1406409111
Prof. Dr. Susana Andrade
Institute of Biochemistry
BIOSS Centre for Biological Signalling Studies
University of Freiburg
Phone: +49 (0)761/203-8719
Katrin Albaum | Albert-Ludwigs-Universität Freiburg
New risk factors for anxiety disorders
24.02.2017 | Julius-Maximilians-Universität Würzburg
Stingless bees have their nests protected by soldiers
24.02.2017 | Johannes Gutenberg-Universität Mainz
In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".
Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
24.02.2017 | Life Sciences
24.02.2017 | Life Sciences
24.02.2017 | Trade Fair News