Moderate concentrations of the alcohol 2,2,2-trifluoroethanol (TFE) cause the cou
pled unfoldingand dissociation into subunits of the homotetrameric
potassium channel KcsA, in a
process that is
partiallyirreversible when the
protein is solubilized in
plain dodecyl
![](/images/gifchars/beta2.gif)
-
D-maltoside (DDM) micelles [Barrera et al.(2005)
Biochemistry 44, 14344-52]. Here we re
port that the transition from the folded tetramer to theunfolded monomer becomes com
pletely reversible when KcsA is solubilized in mixed micelles com
posedof the detergent DDM and the li
pids DOPE (1,2-dioleoyl-
sn-glycero-3-
phos
phoethanolamine) and DOPG(1,2-dioleoyl-
sn-glycero-3-[
phos
pho-
rac-(1-glycerol)]). This result suggests that li
pids may act as effectorsin the tetramerization of KcsA. The observed reversibility allowed the determination of the standard freeenergy of the folding reaction of KcsA:
G = 30.5 ± 3.1 kcal·mol
-1. We also observed that,
prior to theunfolding of the tetramer, the
presence of lower TFE concentrations causes the disassembly ofsu
pramolecular clusters of KcsA into the individual tetrameric molecules. Within the limits of ex
perimentalresolution, this is also a reversible
process, but unlike the tetramer to monomer transition from above, thelevel of clustering is not influenced by the
presence of solubilized li
pids. These observations suggest adistinct role of the li
pids in the different in vitro assembly ste
ps (folding/tetramerization and clustering)of KcsA.