Passage
The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a chloride ion channel involved in the production of mucus, sweat, and digestive fluids. CFTR is composed of five domains (Figure 1) : Two transmembrane domains (TMD1 and TMD2) , two nucleotide binding domains (NBD1 and NBD2) , and one regulatory domain (R domain) .
Figure 1 Schematic diagram of CFTR domainsThe NBD domains regulate CFTR activity by binding ATP, which causes a conformational change in the TMD domains. This change allows chloride ions to leave cells by passively crossing the membrane down their concentration gradient. The R domain regulates activity further through dynamic phosphorylation at several positions. The movement of chloride ions facilitates the movement of water out of the cell by osmotic pressure and helps keep secretions thin.Cystic fibrosis (CF) arises from recessively inherited mutations in the CFTR gene. The most common mutation is a three-base-pair deletion that removes a phenylalanine residue at position 508 in NBD1 (ΔF508) . This mutation causes the protein to fold incorrectly, making it more susceptible to degradation by proteases. The resulting decrease in CFTR abundance inhibits chloride ion transport, leading to thickening of normally thin secretions and increased risk of life-threatening pulmonary infections.
-A scientist proposed that phosphorylation of the R domain increases CFTR activity. Which of the following functional groups in the R domain could be removed by mutation to test this hypothesis in vivo?

Question

Passage
The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a chloride ion channel involved in the production of mucus, sweat, and digestive fluids. CFTR is composed of five domains (Figure 1) : Two transmembrane domains (TMD1 and TMD2) , two nucleotide binding domains (NBD1 and NBD2) , and one regulatory domain (R domain) .

Figure 1 Schematic diagram of CFTR domainsThe NBD domains regulate CFTR activity by binding ATP, which causes a conformational change in the TMD domains. This change allows chloride ions to leave cells by passively crossing the membrane down their concentration gradient. The R domain regulates activity further through dynamic phosphorylation at several positions. The movement of chloride ions facilitates the movement of water out of the cell by osmotic pressure and helps keep secretions thin.Cystic fibrosis (CF) arises from recessively inherited mutations in the CFTR gene. The most common mutation is a three-base-pair deletion that removes a phenylalanine residue at position 508 in NBD1 (ΔF508) . This mutation causes the protein to fold incorrectly, making it more susceptible to degradation by proteases. The resulting decrease in CFTR abundance inhibits chloride ion transport, leading to thickening of normally thin secretions and increased risk of life-threatening pulmonary infections.
-A scientist proposed that phosphorylation of the R domain increases CFTR activity. Which of the following functional groups in the R domain could be removed by mutation to test this hypothesis in vivo?

Quizplus · Accepted Answer

11ecba2d_0e8a_ba80_a3bf_f317b928bf29_MD0008_00 Post-translational modifications are covalent additions of non-amino acid groups to a protein. They are catalyzed by enzymes and generally only occur at specific amino acid residues. Phosphorylation is a common post-translational modification that is facilitated by protein kinase enzymes. Phosphorylation occurs at serine, threonine, and tyrosine residues, each of which contains a hydroxyl group in its side chain. Protein kinases catalyze the nucleophilic reaction in which the hydroxyl group on the amino acid side chain takes a phosphate group from ATP. The effects of a post-translational modification (eg, phosphorylation) on protein activity can be investigated by generating a mutated form of the protein that cannot be modified. In the given scenario, the phosphorylated amino acids in the protein should be replaced with amino acids that cannot be phosphorylated by protein kinases in a living system (in vivo). The new amino acids should lack hydroxyl groups to prevent phosphorylation but should otherwise be as similar to the original amino acids as possible to preserve protein structure (ie, tyrosine to phenylalanine, serine and threonine to alanine). Scientists can then compare the functional activity of the unphosphorylated protein to the activity of the phosphorylated protein and determine which is higher. (Choice A) The amide groups of asparagines and glutamine may be glycosylated (usually asparagine) but are rarely phosphorylated. (Choice C) Thiol is the functional group of cysteine. Although it can act as a nucleophile, cysteine rarely participates in phosphorylation. (Choice D) Carboxylic acids, found in aspartate and glutamate, are rarely phosphorylated. Educational objective: Post-translational modifications are covalent additions of non-amino acid groups to proteins. They generally occur at specific residues that have the necessary chemical properties. Phosphorylation occurs almost exclusively at the hydroxyl groups of serine, threonine, and tyrosine residues.

Passage the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Protein Is a a Chloride