analysis-protein-folding-transport-degradation-living-cells

Analysis of Protein Folding, Transport, and Degradation in Living Cells by Radioactive Pulse Chase

Radioactive pulse-chase labeling is a powerful tool for studying the conformational maturation, the transport to their functional cellular location, and ...

Utrecht University

Synonymous single nucleotide polymorphisms (sSNPs) are considered neutral for protein function, as by definition they exchange only codons, not amino acids. We identified an sSNP that modifies the local translation speed of the cystic fibrosis transmembrane conductance regulator (CFTR), leading to detrimental changes to protein stability and function. This sSNP introduces a codon pairing to a low-abundance tRNA that is particularly rare in human bronchial epithelia, but not in other human tissues, suggesting tissue-specific effects of this sSNP. Up-regulation of the tRNA cognate to the mutated codon counteracts the effects of the sSNP and rescues protein conformation and function. Our results highlight the wide-ranging impact of sSNPs, which invert the programmed local speed of mRNA translation and provide direct evidence for the central role of cellular tRNA levels in mediating the actions of sSNPs in a tissue-specific manner.

Alteration of protein function by a silent polymorphism linked to tRNA abundance.

Pharmacological intervention to treat the lethal genetic disease cystic fibrosis has become reality, even for the severe, most common folding mutant F508del CFTR. CFTR defects range from absence of the protein, misfolding that leads to degradation rather than cell-surface localization (such as F508del), to functional chloride-channel defects on the cell surface. Corrector and potentiator drugs improve cell-surface location and channel activity, respectively, and combination therapy of two correctors and a potentiator have shown synergy. Several combinations are in the drug-development pipeline and although the primary defect is not repaired, rescue levels are reaching those resembling a cure for CF. Combination therapy with correctors may also improve functional CFTR mutants and benefit patients on potentiator therapy.

Correcting CFTR folding defects by small-molecule correctors to cure cystic fibrosis.

Cystic fibrosis is caused by mutations in the  gene, which are subdivided into six classes. Mutants of classes III and IV reach the cell surface but have limited function. Most class-III and class-IV mutants respond well to the recently approved potentiator VX-770, which opens the channel. We here revisited function and folding of some class-IV mutants and discovered that R347P is the only one that leads to major defects in folding. By this criterion and by its functional response to corrector drug VX-809, R347P qualifies also as a class-II mutation. Other class-IV mutants folded like wild-type CFTR and responded similarly to VX-809, demonstrating how function and folding are connected. Studies on both types of defects complement each other in understanding how compounds improve mutant CFTR function. This provides an attractive unbiased approach for characterizing mode of action of novel therapeutic compounds and helps address which drugs are efficacious for each cystic fibrosis disease variant.

Article	Year
Alteration of protein function by a silent polymorphism linked to tRNA abundance. PLoS biology\| PubMed ID: 28510592	2017
Correcting CFTR folding defects by small-molecule correctors to cure cystic fibrosis. Current opinion in pharmacology\| PubMed ID: 29055231	2017
Folding-function relationship of the most common cystic fibrosis-causing CFTR conductance mutants. Life science alliance\| PubMed ID: 30659068	2019

Bertrand Kleizen

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