Metamorphic Response of the CLIC1 Chloride Intracellular Ion Channel Protein upon Membrane Interaction

摘要

A striking feature of the CLIC (chloride intracellular channel) protein family is the ability of itsnmembers to convert between a soluble state and an integral membrane channel form. Direct evidence of thenstructural transition required for the CLIC protein to autonomously insert into the membrane is lacking,nlargely because of the challenge of probing the conformation of the membrane-bound protein. However,ninsights into the CLIC transmembrane form can be gained by biophysical methods such as fluorescencenresonance energy transfer (FRET) spectroscopy. This approach was used to measure distances fromntryptophan 35, located within the CLIC1 putative N-domain transmembrane region, to three native cysteinenresidues within the C-terminal domain. These distances were computed both in aqueous solution and upon thenaddition of membrane vesicles. The FRET distances were used as constraints for modeling of a structure fornthe CLIC1 integral membrane form. The data are suggestive of a large conformational unfolding occurringnbetween the N- and C-domains of CLIC1 upon interaction with the membrane. Consistent with previousnfindings, theN-terminal domain of CLIC1 is likely to insert into the lipid bilayer, while the C-domain remainsnin solution on the extravesicular side of the membrane.