The cystic fibrosis transmembrane conductance regulator (CFTR) anion channel is essential to maintain fluid homeostasis in key organs. Functional impairment of CFTR due to mutations in the cftr gene leads to cystic fibrosis. Here, we show that the first nucleotide-binding domain (NBD1) of CFTR can spontaneously adopt an alternate conformation that departs from the canonical NBD fold previously observed. Crystallography reveals that this conformation involves a topological reorganization of NBD1. Single-molecule fluorescence resonance energy transfer microscopy shows that the equilibrium between the conformations is regulated by adenosine triphosphate binding. However, under destabilizing conditions, such as the disease-causing mutation F508del, this conformational flexibility enables unfolding of the β-subdomain. Our data indicate that, in wild-type CFTR, this conformational transition of NBD1 regulates channel function, but, in the presence of the F508del mutation, it allows domain misfolding and subsequent protein degradation. Our work provides a framework to design conformation-specific therapeutics to prevent noxious transitions.
Bibliographical noteFunding Information:
We thank C. R. O’Riordan for C127 cells, J. Kappes for HEK293 CFTR cells and J. R. Riordan, T. Jensen and CF Foundation Therapeutics for anti-CFTR antibodies. C.G. acknowledges support by the Fonds Forton, Welbio (grant no. CR-2012S-04R), Vaincre la Mucoviscidose, Mukoviszidose e.V., the Association Luxembourgeoise de Lutte contre la Mucoviscidose, ABCF2, Chiesi Fondation, the Cystic Fibrosis Foundation, Fondation Air Liquide and Fondation ULB. D.N.S acknowledges support from the CF Trust and CF Foundation Therapeutics. J.S. acknowledges support from Instruct-ERIC, part of the European Strategy Forum on Research Infrastructures (ESFRI), Instruct-ULTRA (EU H2020 grant no. 731005) and the Research Foundation—Flanders (FWO) for support with nanobody discovery. C.G. is a senior Research Associate of the FRS-FNRS. D.S. was a fellow of the FRIA. We acknowledge Diamond Light Source for time on beamlines i02, i04 and i24 under proposals 12718 and 9426. We are grateful to H. Remaut and B. Kobilka for careful reading of the manuscript. We thank F. Sobott and J. Ault of the Biomolecular Mass Spectrometry department in the Astbury Centre for their support and assistance in this work, as well as the BBSRC (BB/M012573/1) for funding.
© 2021, The Author(s), under exclusive licence to Springer Nature America, Inc.
- ion channels
- protein folding
- single-molecule biophysics
- x-ray crystallography