Characterization of the mutations associated with Cystic Fibrosis in the C-terminal region of the Cystic Fibrosis transmembrane conductance regulator (CFTR)

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Abstract

Cystic fibrosis is a major inherited disease associated with morbidity and mortality around the globe. CFTR is an important ion channel that regulates the movement of chloride ions. Thus, mutations in the CFTR gene disrupt the transport of epithelial fluid and result in the development of classical symptoms such as impaired lung function. Among the protein domains involved in CFTR localisation and function, mutations affecting the C-terminal region have been implicated in cystic fibrosis. Understanding the impact of the mutations is important in developing effective therapeutic approaches. This study determined the impact of six cystic fibrosis related single amino acid substitutions (D1445N, R1453W, Q1463H, K1468N, L1480P, and C1458A) on the overall conformation of the C-terminal peptide and on the interaction between CFTR and the scaffold protein NHERF1, with specific focus on the PDZ1 domain. The effects of single amino acid substitution were investigated by several biochemical and biophysical analyses, with results for Circular Dichroism CD, SEC-MALS-QELS, SPR, and pull down assay being described in this thesis. The data showed that the mutations did not affect the successful creation, amplification and production of the C-terminal42aa CFTR peptides nor their overall secondary structure. The PDZ1 domain of the NHERF1 was also successfully created, expressed and purified. The single amino acid mutations were shown to alter this protein-protein interaction in a predictable way. When compared to robust binding of the wild-type C-terminus CFTR with NHERF1 PDZ1, the single amino acid mutations in Q1463H, R1453W, D1445N, K1468N, and C1458A constructs did not prevent binding but instead altered the strength of the protein-protein interaction. In contrast, a major difference occurred in the binding affinity between NHERF1 PDZ1 and the L1480P mutation. The phenotypic manifestation of a given CFTR mutation in Cystic Fibrosis is complex and heavily dependent on the impact of the mutation on the different functions and interactome of CFTR. In the light of the evidence presented in this thesis, future studies should aim to fully characterise the effect of the C-terminal CFTR mutations on its cellular interactions and to extend these findings to systems closer to in-vivo such as organoids.

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