A protein problem causes cystic fibrosis
Cystic fibrosis is one of the most common conditions caused by a defective transport protein. Around 9,000 people in the UK have this life-shortening condition, which has no cure. People who are affected often have repeated chest infections and problems with their digestive system.
The protein involved – the cystic fibrosis transmembrane conductance regulator, or CFTR – was named after the condition. It regulates the movement of chloride ions. A faulty version of the protein causes a change in the composition of sweat and of mucus secretions in the throat, lungs and intestines.
The CFTR protein is large (1,480 amino acids) and almost 2,000 different genetic mutations are known. The most common, which accounts for two-thirds of all cases of cystic fibrosis, is a deletion of three DNA bases in the CFTR protein. This removes a single amino acid, a phenylalanine, which is the 508th amino acid in the sequence. The altered protein does not fold properly and so is broken down by the cell. Other mutations produce proteins that are too short or that are present in the cell membrane but don’t work as they should.