A defective flexible loop contributes to the processing and gating defects of the predominant cystic fibrosis‐causing mutation

Abstract

People with the genetic disease cystic fibrosis (CF) often carry a deletion mutation ∆F508 on the gene encoding the CF transmembrane conductance regulator (CFTR) Cl− channel. This mutation greatly reduces the CFTR maturation process and slows the channel opening rate. Here, we investigate whether residues near F508 contribute to these defects in ∆F508‐CFTR. Most deletion mutations, but not alanine substitutions, of individual residues from positions 503 to 513 impaired CFTR maturation. Interestingly, only protein processing of ∆Y512‐CFTR, like that of ∆F508‐CFTR, was greatly improved by low‐temperature culture at 27°C or small‐molecule corrector C18. The 2 mutant Cl− channels were equally slow to open, suggesting that they may share common structural flaws. Studies on the H3‐H4 loop that links residues F508 and Y512 demonstrate that G509A/V510G mutations, moving G5091 position backward in the loop, markedly enhanced ∆F508‐CFTR maturation and opening rate while promoting protein stability and persistence of the H3 helix in ∆F508 nucleotide‐binding domain 1. Moreover, V510A/S511A mutations noticeably increased ∆Y512‐CFTR maturation at 27°C and its opening rate. Thus, loop abnormalities may contribute to ∆F508‐ and ∆Y512‐CFTR defects. Importantly, correcting defects from G509 displacement in ∆F508‐CFTR may offer a new avenue for drug discovery and CF treatments.—Chen, X., Zhu, S., Zhenin, M., Xu, W., Bose, S. J., Wong, M. P.‐F., Leung, G. P. H., Senderowitz, H., Chen, J.‐H. A defective flexible loop contributes to the processing and gating defects of the predominant cystic fibrosis‐causing mutation. FASEB J. 33, 5126–5142 (2019). http://www.fasebj.org

Novel frameshift variant of the CFTR gene: S511Lfs*2 from phenotype to molecular predictions

“…Additional studies demonstrated that a single-residue deletion in the region 491-525 elicits an array of abnormalities in CFTR function [26]. Although it was found that specifically the amino acids V510 and S511 deletions did not cause problems in the processing of the CFTR protein, our data show that the new mutation S511Lfs*2 is caused by the deletion of two T nucleotides in different codons.…”

“…3), which is responsible by the channel activation and thus essential for the functionality of the protein. The loss of this domain was predicted based on sequence and structural analysis, since this domain was not resolved by the Electron Cryomicroscopy (cryo-EM) structure [20,26].…”

CFTR dysfunction leads to defective bacterial eradication on cystic fibrosis airways

“…CF-associated mutations diminish CFTR function primarily by reducing 1) mRNA synthesis, 2) protein expression, 3) channel regulation and 4) channel conductance, or by increasing 5) protein degradation at the cell membrane ( Amaral and Farinha, 2013 ). For example, the most prevalent CF mutation ΔF508 by introducing intrinsic structural flaws ( Chen et al, 2019 ) blocks CFTR protein expression at the cell membrane ( Cheng et al, 1990 ), whereas ΔF508, G551D and G1349D mutations greatly decrease channel activity ( Dalemans et al, 1991 ; Cai and Sheppard, 2002 ; Cai et al, 2006 ; Bompadre et al, 2007 ; Chen et al, 2009 ; Chen et al, 2017 ) with further alterations in channel responses to gating potentiators ( Hwang et al, 1997 ; Cai and Sheppard, 2002 ; Cai et al, 2006 ; Bompadre et al, 2007 ) and intracellular pH ( Chen et al, 2009 ; Chen et al, 2017 ). Therefore, the current drug therapy for CF aims to elevate the protein expression and channel activity of mutant CFTRs by correctors and potentiators, respectively ( Bose et al, 2020 ).…”