Unfolding of a ClC chloride transporter retains memory of its evolutionary history

• Published in: Nature chemical biology Vol. 14; no. 5; pp. 489 - 496
• Main Authors: Min, Duyoung, Jefferson, Robert E., Qi, Yifei, Wang, Jing Yang, Arbing, Mark A., Im, Wonpil, Bowie, James U.
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 01.05.2018; Nature Publishing Group
• Subjects: Biochemical Engineering; Biochemistry; Bioorganic Chemistry; Cell Biology; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Chloride channels; Complexity; E coli; Folding; Helices; Hereditary diseases; Homeostasis; Membrane proteins; Mutation; Proteins
• ISSN: 1552-4450; 1552-4469; 1552-4469
• DOI: 10.1038/s41589-018-0025-4

ClC chloride channels and transporters are important for chloride homeostasis in species from bacteria to human. Mutations in ClC proteins cause genetically inherited diseases, some of which are likely to involve folding defects. The ClC proteins present a challenging and unusual biological folding problem because they are large membrane proteins possessing a complex architecture, with many reentrant helices that go only partway through membrane and loop back out. Here we were able to examine the unfolding of the Escherichia coli ClC transporter, ClC-ec1, using single-molecule forced unfolding methods. We found that the protein could be separated into two stable halves that unfolded independently. The independence of the two domains is consistent with an evolutionary model in which the two halves arose from independently folding subunits that later fused together. Maintaining smaller folding domains of lesser complexity within large membrane proteins may be an advantageous strategy to avoid misfolding traps. A single-molecule forced unfolding of E. coli chloride transporter ClC-ec1 shows that the N- and C-terminal halves of the protein unfold independently, with exposed polar surfaces stabilized by membrane lipid head groups and water.