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CFTR is a monomer: biochemical and functional evidence
J-H Chen1, X-B Chang, A A Aleksandrov
1Mayo Foundation and Mayo Clinic Scottsdale, S. C. Johnson Medical Research Center, 13400 E. Shea Blvd., Scottsdale, AZ 85259, USA.
The Journal of Membrane Biology
|August 13, 2002
Summary
The cystic fibrosis transmembrane conductance regulator (CFTR) protein functions as a monomer, not a multimer. This study confirms CFTR
Area of Science:
- Molecular biology
- Cell biology
- Ion channel function
Background:
- The cystic fibrosis transmembrane conductance regulator (CFTR) protein forms a regulated chloride channel.
- The oligomeric state of the CFTR protein, crucial for its function, remains undetermined.
Purpose of the Study:
- To determine the number of CFTR polypeptides required for chloride channel formation.
- To investigate the assembly and functional interactions of CFTR subunits.
Main Methods:
- Biochemical assays, including sucrose gradient sedimentation.
- Functional assays using planar lipid bilayers.
- Cellular co-expression studies with epitope-tagged CFTR.
- Immunoprecipitation and nickel affinity binding experiments.
Main Results:
- CFTR sediments as a monomer in sucrose gradients, indicating a single polypeptide unit.
- Co-expression of differently tagged CFTR variants showed no evidence of self-assembly.
- Wild-type and DF508 mutant CFTR did not influence each other's trafficking through the secretory pathway.
- No hybrid channels were observed when fusing vesicles from cells expressing different CFTR variants.
Conclusions:
- The CFTR chloride channel is formed by a single CFTR polypeptide (monomer).
- CFTR does not appear to co-assemble with itself or other CFTR variants in the endoplasmic reticulum or at the plasma membrane.
- These findings clarify the molecular composition of the CFTR channel.