Escherichia coli OmpA retains a folded structure in the presence of sodiumdodecyl sulfate due to a high kinetic barrier to unfolding

Escherichia coli OmpA can be solubilized by sodium dodecyl sulfate (SDS) in its folded structure, and it unfolds upon heating. Although the heat-denat ured OmpA remains unfolded after lowering the temperature. the addition of a non-ionic surfactant, octyl glucoside results in refolding of unfolded Om pA. In the present study, we investigated the refolding kinetics of OmpA in a mixed surfactant system of SDS and octyl glucoside using far- and near-U V circular dichroism and fluorescence spectroscopies. We found four kinetic phases in the refolding reaction, which logarithmically depended on the we ight fraction of octyl glucoside. We also examined the unfolding kinetics o f OmpA upon heating in the presence of SDS by temperature jump experiments. A comparison of the rate constants for the refolding and the unfolding rea ctions in SDS-only solution at 30 degreesC revealed that the folded form of OmpA in SDS solution is less stable than the unfolding form, and that the unfolding is virtually unobservable near room temperature due to a high kin etic barrier. (C) 2001 Elsevier Science B.V. All rights reserved.