Epithelial Chloride Channels 3&4 Flashcards
What did rommens et al discover regarding CF 1989
Identification of CF gene
What did Riordan et al in 1989 discover regarding CF
cDNA of CF gene
What did Kerem et al in 1989 discover regarding CF
Genetic analysis of CF gene
Where is the CF gene found
Human chromosome 7
How long is the CF gene
250,000 base pairs of DNA
What is the CF gene protein called
Cystic fibrosis transmemrbrane conductance regulator
What is the commonest CF mutation
Fetoalanine deletion mutation at 508 in 70% of CF on chromosome 7
What 4 epithelial tissues are affected by CF
Skin
Lung
Gut
Pancreas
What is the CFTR a family of and why was this a surprise
ATP binding cassette family of transport protein (structural homology of this protein type) - surprise as mostly found in bacteria
This family use ATP to pump ions out of the cell.
What is the structure of CFTR
2 hydrophobic membrane spanning domains (anchors to cell membrane) - comprised of 6 alpha helixes
2 nucleotide binding domains - bind and hydrolyse ATP (NBD1 is where the fenylalanine 508 is missing in CF patients)
What is the unique Regulatory domain role
The phosphorylation site for PKA for the CFTR
What did Rich et al 1990 discover regarding CF
Changing CF CFTR gene with normal one corrects defective chloride channel regulation in CF airway epithelial cells.
Also transfected normal CFTR with F508 CFTR and it did not induce appearance of CI currents
What were the Cl channel type seen by Rich et al 1990
Channels induced by CFTR expression very similar to SLCCs not ORCCs.
What actually is CFTR
SLCC - CFTR is a low conductance cAMP-activated chloride channel.
How was CFTR confirmed to be SLCC by bear et al 1992
Used S9 insect line which is a cell containing no channels. They then added CFTR mRNA to make the CFTR protein purified.
CFTR is mixed with phsopholipds to get them into phospholipid vesicles.
This is then rubbed on a plate to form a phospholipid bilayer.
This allows CFTR to sit in the phospholipd bilayer where currents can take place to asses the channel characteristics.
Found cAMP activated SLCCs - final proof than CFTR is a low conductance cAMP-activated chloride channel.
What did Kartner et al discover regarding CFTR in sweat glands in 1992
F508 CFTR was not found in apical membrane - first indication that CF may be due to absence of Cl channels rather than defects in them
What did Denning et al in 1992 find out regarding CFTR in lung epithelium
Not present, backing kartner et al.
Also found that by lowering the temp that it allows F508 mutated CFTR to locate to the apical membrane and it also retained some function. Therefore - DeltaF508 mutation causes trafficking issue not a functional problem
What did sheppard et al in 1993 find out regarding CFTR
Identification of 3 membrane spanning domains which effect arginine residues, as arginine is positive, this results in a reduced currents going through the cAMP-activated SLCC channels.
Therefore - arginine residues possibly determine Cl conductivity of channel
What was found by Cotten and welsh in 1999 regarding CFTR pore architecture
They stated that the pore architectures is based on cationic and anionic amino acid residues - when swapping arginine (+) for aspartate (-) then it destabilises the channel and stops it working. But when swapped both the arg for asp at both sides it maintains the channel.
What are the 6 sections of CFTR
2 - membrane spanning domains (MSD1 and 2)
2 - nucleotide binding domains (NBD1 and NBD2)
R domain
Glycosilation - quality control passed via golgi apparatus and ready to be used.
What activates the CFTR
ATP on both NBD
PKA on the R domain
What are the 4 areas that the CFTR can be affected causing CF
Genetic defect - protein production
Processing in golgi apparatus
Regulation - ATP or PKA issue
Conduction - issue in getting chloride through channel (e.g. channel architecture)
Why is CF difficult to do studies on
No natural animal model
Mice have calcium activated Cl channels in lungs so they take on CFTR role when knocked out so the KO mice area symptomatic
Who made the first CFTR KO mouse
Koller 1992
What did Kollers CFTR KO mouse show
GI obstructions - and failure to thrive.
Only living about 40 days
What did Gabriel et al discover regarding ORCCs and CFTR in 1993
ORCC activation only happens by PKA when CFTR is present in cells
What did Jovov et al discover with regards to ORCC and CFTR with the mutant G551D (5% of CF)
Went put into lipid bilayers it also showed that functional CFTR expression is required for ORCC activation by PKA and ATP
Therefore - CFTR is needed to regulate ORCCs
So in summary what is the role of the CFTR
Small linear conductance chloride channel whos added role is to regulate the outward regulating chloride channels.
What is the commonest CF infection
Pseudomonas aeruginosa