Question

The majority of alleles responsible for CF in the United States contain the same genetic alteration, designated F508. What is the significance of this alteration and how does it lead to CF?

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Answer 1

Cystic fibrosis is associated with a defect in epithelial chloride ion transport which is caused by mutations in a membrane protein called CFTR (cystic fibrosis transmembrane conductance regulator). Heterologous expression of CFTR produces cyclicAMP-sensitive Cl(-)-channel activity. The deletion of phenylalanine at amino-acid position 508 in CFTR (delta F508 CFTR) is the most common mutation in cystic fibrosis. This CF-causing mutation, the deletion of phenylalanine 508 (F508), is located in the N-terminal cytoplasmic NBD1 (5–9). This single amino acid deletion results in a dramatic reduction of mature, plasma membrane resident CFTR. It has been proposed that this mutation prevents glycoprotein maturation and its transport to its normal cellular location. The delta F508 mutation has two major consequences, an abnormal translocation of the CFTR protein which limits membrane insertion, and an abnormal function in mediating Cl- transport causing cystic fibrosis.

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