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Cystic Fibrosis Analysis

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To understand the effects that Cystic Fibrosis has, it is important to discuss CFTR synthesis and trafficking. Mutations in the CFTR results in protein misfolding, causing a defect in cellular processing and trafficking that targets the protein for degradation and reduces the quantity of CFTR at the cell surface [56]. In order for the CFTR to function correctly, then it must be synthesized, folded, and transported to the apical membrane of the cell without problem. The CFTR passes through quality control systems to get rid of misfolded proteins that would not function properly or that could become damaged [16]. It is apparent that only 33% of CFTR folds correctly and is allowed to leave the endoplasmic reticulum [8]. The nucleus is the site …show more content…

Chaperones are proteins that ensure the correct folding of the CFTR within the endoplasmic reticulum. Hsp70 is an important cytosolic chaperone that complexes with CFTR and reduces aggregation [5]. The CFTR passes through the endoplasmic reticulum-associated degradation (ERAD) after folding in the ER. This quality control system involves the ubiquitin proteasome system (UPS) for which CFTR is a substrate [16]. If a protein is molded and targeted for degradation, then ubiquitin will covalently attach to lysine residues on the CFTR. Three enzymes are required for the process of ubiquitylation: E1 ubiquitin activating enzymes, E2 ubiquitin conjugating enzymes, and E3 ubiquitin protein ligases. E1 enzymes are activated through hydrolysis of ATP, which creates an activated ubiquitin that is transferred to an E2 active site. The activated ubiquitin is then covalently bound to a lysine on the protein by an E3 ligase. A polyubiquitin chain is then formed as ubiquitin molecules link together, and if there are four or more then the misfolded CFTR chain is removed form the ER membrane and targeted for degradation by the 26S proteasome …show more content…

One system detects defects in the cytosolic parts of the CFTR while the other detects defects within the endoplasmic reticulum membrane. It is apparent that ubiquitylating proteins work with specific factors in order to detect misfolding. For example, Hsp70 detects mutations in the cytosolic regions of the CFTR. It is suspected that Hsp70 keeps the CFTR soluble until the E3 ligase CHIP binds with it. The complex that forms between these two redirects the CFTR to the degradation pathway. Derlin-1 is involved with detecting defects in the endoplasmic reticulum membrane and is involved in the retro-translocation of CFTR from the endoplasmic reticulum so that it can be send to the proteasome for degradation [20]. If the CFTR protein is folded correctly within the endoplasmic reticulum, then it is sent to the Golgi apparatus. The coat protein complex II (COPII), which is found within the ER membrane, helps to maintain the correct CFTR structure and location, conformation, and protein-protein interactions as this occurs. Final processing for the CFTR is carried out within the Golgi, as the CFTR replaces a mannose-enriched side chain with a mature complex oligosaccharide side chain. After this is completed, the CFTR is moved to the apical membrane where it has a half-life of 12 to 24 hours. If a CFTR is functioning poorly within the membrane, then it can be recognized by Hsc70 and then

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