Studying Solute Carriers in Real-time

Solute carriers are important proteins, which reside in the membranes of cells. It is their function to allow access of molecules into the interior of a cell, which would otherwise not be able to cross cellular membranes. Nutrients such as glucose, for instance, can only enter a cell because of the existence of dedicated carriers (e.g., glucose transporters). For this reason, these proteins are essential for the thriving and survival of a cell. It is, thus, not surprising that many inherited diseases are caused by mutations in the genes, which encode solute carriers when these lead to carrier malfunction. Therefore, there is an urgent need to identify new drug targets and to develop novel strategies to treat disorders caused by disease causing transporter variants. However, the success of such efforts relies on an in-depth knowledge of the mechanisms, which give rise to the observed pathology. Since all solute carriers operate on the millisecond time scale, the required insights can only be obtained by methods that provide adequate temporal resolution. The objective of the current project is, thus, to track the operation of solute carriers in real time. To this end we will use two methods, which provide the needed temporal precision. These are measurements of the small electrical currents, which pass through solute carriers and measurements of the changes in the electric capacitance of a cell induced by these transporters. Changes in the amplitude of the electric current and capacitance report on processes such as binding of the transported molecules to the carrier or on the molecular rearrangements the carrier must undergo to afford translocation of its cargo. Each of these processes constitutes a partial reaction in the overall transport cycle of a transporter. Importantly, the information provided by these two methods is complementary in that one partial reaction can be tracked by one method and another by the other method. Together these two approaches (current and capacitance measurements) allow for monitoring in real time all essential reactions underlying solute transport and to identify those processes which are impaired in the disease causing carrier variants. The latter information may pave the way towards pharmacological remedies. In addition, because capacitance recordings can also provide insights on the action of drugs, which target solute carriers we will use this method to unravel the mechanism by which drugs referred to as allosteric modulators affect the function of these proteins. Allosteric modulators to not bind where the transported molecule binds and they are of interest because they have the potential to rescue the function of impaired carriers.