Structural cues involved in endoplasmic reticulum degradation of G85E and G91R mutant cystic fibrosis transmembrane conductance regulator.

Published

Journal Article

Abnormal folding of mutant cystic fibrosis transmembrane conductance regulator (CFTR) and subsequent degradation in the endoplasmic reticulum is the basis for most cases of cystic fibrosis. Structural differences between wild-type (WT) and mutant proteins, however, remain unknown. Here we examine the intracellular trafficking, degradation, and transmembrane topology of two mutant CFTR proteins, G85E and G91R, each of which contains an additional charged residue within the first putative transmembrane helix (TM1). In microinjected Xenopus laevis oocytes, these mutations markedly disrupted CFTR plasma membrane chloride channel activity. G85E and G91R mutants (but not a conservative mutant, G91A) failed to acquire complex N-linked carbohydrates, and were rapidly degraded before reaching the Golgi complex thus exhibiting a trafficking phenotype similar to DeltaF508 CFTR. Topologic analysis revealed that neither G85E nor G91R mutations disrupted CFTR NH2 terminus transmembrane topology. Instead, WT as well as mutant TM1 spanned the membrane in the predicted C-trans (type II) orientation, and residues 85E and 91R were localized within or adjacent to the plane of the lipid bilayer. To understand how these charged residues might provide structural cues for ER degradation, we examined the stability of WT, G85E, and G91R CFTR proteins truncated at codons 188, 393, 589, or 836 (after TM2, TM6, the first nucleotide binding domain, or the R domain, respectively). These results indicated that G85E and G91R mutations affected CFTR folding, not by gross disruption of transmembrane assembly, but rather through insertion of a charged residue within the plane of the bilayer, which in turn influenced higher order tertiary structure.

Full Text

Duke Authors

Cited Authors

  • Xiong, X; Bragin, A; Widdicombe, JH; Cohn, J; Skach, WR

Published Date

  • September 1, 1997

Published In

Volume / Issue

  • 100 / 5

Start / End Page

  • 1079 - 1088

PubMed ID

  • 9276724

Pubmed Central ID

  • 9276724

International Standard Serial Number (ISSN)

  • 0021-9738

Digital Object Identifier (DOI)

  • 10.1172/JCI119618

Language

  • eng

Conference Location

  • United States