# Molecular Pathophysiology of Cystic Fibrosis

> **NIH NIH R01** · UNIVERSITY OF MISSOURI-COLUMBIA · 2020 · $421,319

## Abstract

Loss-of-function mutations in the cftr gene are the root cause of cystic fibrosis (CF), the
second most common life-shortening genetic disease in the US. As a member of the ABC
(ATP Binding Cassette) transporter superfamily, the CFTR protein comprises two
transmembrane domains (TMD1 and TMD2), each followed by a nucleotide binding
domain (NBD1 and NBD2 respectively) characterized by the canonical Walker A and B
motifs for ATP binding/hydrolysis, and a signature sequence (i.e., LSGGQ) that plays a
critical role for the formation of a head-to-tail NBD dimer upon ATP binding. CFTR is
unique in that, instead of being an active transporter, CFTR is a bona fide ion channel.
Our previous studies have led to a gating mechanism of CFTR that features a
probabilistic relationship between ATP-induced NBD dimerization and gate opening in
the TMDs. Recent solutions of three cryo-EM structures of CFTR, on one hand, dispute
our idea that channel closure does not require a complete separation of the two NBDs, but
on the other hand, support our proposition that NBD dimerization does not guarantee gate
opening. These cryo-EM data lack high temporal resolution, but their exquisite spatial
resolution does offer us an unprecedented opportunity to address several unsettled
questions regarding the functional anatomy of CFTR (Aim 1) such as: What is the
functional significance of completely separated NBDs shown in the cryo-EM structures?
How do the two ATP-binding sites affect each other’s function? The existence of a closed
channel with dimerized NBDs not only demands more thorough studies of the gating
mechanism but also compels us to challenge the long-held view that only the open
channel hydrolyzes ATP. As many of the disease-associated mutations reside in the NBD
dimer interface, and thus are excellent subjects facilitating our investigation into
NBD/TMD coupling, the proposed studies could also reveal the mechanism by which
these mutations cause CF at a molecular level. One important application of our
fundamental studies of CFTR gating is to use the knowledge to explore how drugs or
drug candidates affect different aspects of CFTR gating (Aim 2), and to determine if and to what
extent pathogenic mutations respond to therapeutic reagents (Aim 3). Together with the atomic
structures of CFTR in different states, it is timely to probe how reagents, by binding to different
regions of CFTR, synergistically activate CFTR. Answering this latter question could serve as a
stepping-stone to materialize structure-based drug design.

## Key facts

- **NIH application ID:** 9932375
- **Project number:** 5R01DK055835-19
- **Recipient organization:** UNIVERSITY OF MISSOURI-COLUMBIA
- **Principal Investigator:** Tzyh-Chang Hwang
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $421,319
- **Award type:** 5
- **Project period:** 1999-09-30 → 2023-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9932375

## Citation

> US National Institutes of Health, RePORTER application 9932375, Molecular Pathophysiology of Cystic Fibrosis (5R01DK055835-19). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9932375. Licensed CC0.

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