A team of scientists led by Prof. Dr. Susana Andrade from the Institute of Biochemistry of the University of Freiburg 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 membrane proteins from an archaea, a microorganism that lives under extreme temperature conditions, and isolated them. Already in 2005, the Freiburg researchers shed light on the crystalline three-dimensional structure of a protein from this protein family. Now they imbedded this cloned protein into a layer of lipid molecules. With this setup, the researchers were able to measure the ion currents directly. Prof. Andrade's 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+. "Our in vitro method gives us a level of precision that finally allows us to draw valid conclusions concerning the transport process," stresses Susana Andrade.
"The results can, in a large part, be transferred to the Rhesus proteins from mammals," Andrade continues. 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 level. The researchers tested three Amt proteins that can be found in bacteria, and also determined the speed at 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 the biochemist, who is also a member of the Freiburg Cluster of Excellence "BIOSS Centre for Biological Signalling Studies". (© University of Freiburg, AcademiaNet)