Folding and maturation of the cystic fibrosis related CFTR protein in the ER

Cystic fibrosis (CF) is the most common lethal genetic disease among Caucasians. It is caused by mutations in the CF gene, which encodes the cAMP-regulated CFTR chloride channel, member of the ABC-transporter family. CFTR folding and maturation is a complex process, involving synthesis, integration, and folding of ER lumenal, intramembrane, and cytosolic domains. Chaperones and folding enzymes act on each side of the ER membrane, resulting in a folding and maturation process for which efficiency and speed depend heavily on the cell. When active on the plasma membrane, CFTR associates with many other proteins, which may already bind in the ER, perhaps affecting CFTR folding. The result of this strong dependence on other proteins is a research field full of published controversy, such as folding between 30-100% efficiency, and rapid degradation or no degradation at all. Our proposed project addresses these controversies, because we are convinced that they find their basis in the wealth of interactions CFTR undergoes. Using a systematic approach, and combining assays in intact cells and in a more defined in vitro system, we will address the question of CFTR conformation and the effect of patient mutations on the one hand, and associating proteins on the other hand. We will not only focus on chaperones and folding enzymes but also on proteins known to associate with CFTR on the plasma membrane. Every binding protein is a candidate for affecting folding, maturation, or conformation. The results of our studies will provide answers to questions of CFTR conformational defects and folding efficiencies, and will shed light on controversies. To know in detail how this protein folds and which factors affect its folding will open ways for therapy, as every single patient may need custom treatment, considering not only the particular mutation, but also the cellular make-up of that patient.