INVESTIGATION OF TRANSPORTER AND CHANNEL ACTIVITY OF CLC PROTEINS INVOLVED IN HUMAN GENETIC DISEASES

The CLC family of chloride channels comprises nine members in humans of which at least five are involved in monogenic hereditary diseases. These ion transport proteins are involved in various organs in the transport of chloride ions across biological membranes, a defect of which can cause severe pathological conditions. Significant progress in the understanding of CLC proteins has been made in the last two years. In particular the crystallization of a bacterial CLC protein (CLC-ec1) has opened the possibility of a detailed investigation of the molecular mechanisms of functioning of CLC channels. Furthermore, very recently, it has been revealed that the bacterial protein CLC-ec1 actually is not a chloride ion channel but instead an antiporter of protons and chloride ions. This finding is extremely important for an understanding of the functioning of the human counterparts of the bacterial protein and leads immediately to a series of questions. In this research project three specific questions that are of particular relevance for Dent's disease (that is caused by mutations of CLC-5) and for osteopetrosis (that is caused by mutations of CLC-7) shall be answered: 1. Does CLC-5 have an intrinsic chloride-proton antiport activity? 2. What is the identity of the sensor of intracellular protons? 3. What are the functional properties of CLC-7? The answers to these questions are important for an understanding of the functioning and the malfunctioning of these CLC proteins caused by mutations that lead to Dent's disease and osteopetrosis. No specific treatment exists currently for these diseases. A better knowledge of the biological mechanisms of the molecular components is useful and possibly indispensable for the development of a future treatment.