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
Cells communicate in a dynamic code
19.02.2018 | California Institute of Technology
Studying mitosis' structure to understand the inside of cancer cells
19.02.2018 | Biophysical Society
For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.
In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...
Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale
Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...
For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.
But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...
Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.
The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...
Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters
Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...
15.02.2018 | Event News
13.02.2018 | Event News
12.02.2018 | Event News
19.02.2018 | Materials Sciences
19.02.2018 | Materials Sciences
19.02.2018 | Life Sciences