In case you missed it, there was a groundbreaking achievement in the field of Cystic Fibrosis research last month. Zhe Zhang and Jue Chen from The Rockefeller University in New York published the first structure of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) in the December 1st issue of the journal, Cell(1).
Cystic Fibrosis (CF) is an autosomal recessive disorder defined by mutations in the gene encoding the CFTR(2). The CFTR is a member of the ABC transporter family, and is primarily responsible for the transport of sodium, bicarbonate, and glutathione across epithelial surfaces(3,4). A dysfunction in the protein encoded by this gene leads to a buildup of mucus in the airways of patients with CF. This mucus provides an ideal environment for the colonization of bacteria such as Pseudomonas aeruginosa and Burkholderia cepacia leading to chronic lung infection and ultimate mortality in CF patients(5). Currently, there is no cure for CF.
The CFTR structure was determined by single-particle electron cryo-microscopy (cryo-EM) to a resolution of 3.7 Å (PDB: 5TSI). For these structural studies, the zebrafish homolog of the CFTR protein was used, which has a 55% sequence identity to the human protein. This structure elucidated the key regulatory domains of the CFTR, including the nucleotide-binding domains, the regulatory domain, the anion conduction pathway, as well as the extracellular gate.
Importantly, this work allows the mapping of the disease causing mutations onto the structure, including the DeltaF508 mutation, which is responsible for close to two-thirds of all CF cases worldwide(6). For the first time, the potential structural effects of these mutations can be visualized, which lead to defects in protein folding, ion conduction, and gating. This structure is a paramount step forward in the efforts to design therapeutic strategies to treat and ultimately cure CF.
In this study, membranes containing overexpressed zebrafish CFTR protein were solubilized with 1% LMNG (NG310) and 0.2% CHS (CH210). The protein was purified for Cryo-EM studies using Digitonin. To aid in the vitrification process, 3 mM Fluorinated Fos-Choline 8 (F300F) was used.