The Cystic Fibrosis Drug Discovery and the Structure of the CFTR

General ILL webinar 

Organised by College 8

Wednesday 17 February 2021 at 14h00

"The Cystic Fibrosis Drug Discovery and the Structure of the CFTR"

Oscar Moran

Istituto di Biofisica, Consiglio Nazionale delle Ricerche (CNR)
Genova, Italy
 

Cystic fibrosis (CF), the most common lethal genetic disease in the Caucasian population, is caused by mutations on the gene coding for a 1480-residues membrane integral protein CFTR (cystic fibrosis transmembrane conductance regulator), an anion selective channel that carry chloride and bicarbonate on the apical membrane of secretory epithelium. CFTR regulates salt and water transport, and malfunction of this protein leads to faulty mucus and epithelial surface liquid properties, resulting in poor mucus clearance, with consequent bacterial infections on the airways and obstruction of the pancreas ducts. Mutations in CFTR, classified in six classes according to the effect of the mutation, lead to anion transport defects in epithelium by various mechanisms (failure to synthesize the protein, processing flaws, gating or conductance defects, reduced expression). Among the >1500 mutations reported, the deletion of phenylalanine at position 508 of the CFTR protein (F508del), impairing the CFTR folding, is the most common mutation, being present in ~90% of worldwide CF patients. Several small molecules, called correctors, increase CFTR defective expression at the cell membrane, and small molecules called potentiators enhance the function of the CFTR channel. The potentiator ivacaftor (KalydecoTM) is successfully used for treatment in patients with gating mutations. Formulations of the correctors lumacaftor, tezacaftor and elexacaftor, in combination with ivacaftor (OrkambiTM,  SymdekoTM, TrikaftaTM) have been approved for patients carrying the mutation F508del, with moderate clinical outcomes. To enable the rational discovery of a CF-drugs, structural studies of the entire CFTR protein need to be performed that allow an examination of its architecture and a better understanding of the dynamic arrangements of your domains.  Additionally structural data may yield insights into the consequence of the various mutations that give rise to cystic fibrosis, better identifying the targets for a pharmacological rescue therapy.
We have used small-angle X-ray scattering (SAXS) to study the effects of the binding of ATP to the nucleotide binding domains (the only NBDs structures resolved by X-ray diffraction), and the conformational changes of the regulatory domain by phosphorylation. Although the structure of the complete wild type CFTR has been obtained by cryoEM, the lack of the structure of the F508del-CFTR seriously limits the drug discovery. We have analysed the structure of wild type and F508del CFTR in cell membranes enriched with CFTR, and of purified protein solubilised in detergent.  Our data shows that the general structure of the F508del mutant is significantly different from the native protein. These data seriously questions the validity of any in silico search of new drugs based on the known wild type CFTR structure.

 

Olga Matsarskaia (College 8 Secretary)