Assembly and misassembly of cystic fibrosis transmembrane conductance regulator: folding defects caused by deletion of F508 occur before and after the calnexin-dependent association of membrane spanning domain (MSD) 1 and MSD2.
Cystic fibrosis transmembrane conductance regulator (CFTR) is a polytopic membrane protein that functions as a Cl(-) channel and consists of two membrane spanning domains (MSDs), two cytosolic nucleotide binding domains (NBDs), and a cytosolic regulatory domain. Cytosolic 70-kDa heat shock protein (Hsp70), and endoplasmic reticulum-localized calnexin are chaperones that facilitate CFTR biogenesis. Hsp70 functions in both the cotranslational folding and posttranslational degradation of CFTR. Yet, the mechanism for calnexin action in folding and quality control of CFTR is not clear. Investigation of this question revealed that calnexin is not essential for CFTR or CFTRDeltaF508 degradation. We identified a dependence on calnexin for proper assembly of CFTR's membrane spanning domains. Interestingly, efficient folding of NBD2 was also found to be dependent upon calnexin binding to CFTR. Furthermore, we identified folding defects caused by deletion of F508 that occurred before and after the calnexin-dependent association of MSD1 and MSD2. Early folding defects are evident upon translation of the NBD1 and R-domain and are sensed by the RMA-1 ubiquitin ligase complex.
Rosser
Meredith F N
MF
Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. mrosser@email.unc.edu
Grove
Diane E
DE
Chen
Liling
L
Cyr
Douglas M
DM
D037281:Calnexin / Q000378:metabolism*; D002460:Cell Line; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry* / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D007212:Indolizines / Q000494:pharmacology; D008958:Models, Molecular; D050505:Mutant Proteins / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D017510:Protein Folding / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion / Q000187:drug effects; D054836:Indolizidines
D037281:Calnexin; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D018840:HSP70 Heat-Shock Proteins; D007212:Indolizines; D050505:Mutant Proteins; C093349:cystic fibrosis transmembrane conductance regulator delta F508; C037806:castanospermine; D054836:Indolizidines