Unfolding a transmembrane helix dimer: A FRET study in mixed micelles

Cotranslational folding of membrane proteins probed by arrest-peptide–mediated force measurements

“…In vitro studies have shown that purified membrane proteins can fold from a denatured state (1)(2)(3). Coexpression or coreconstitution of artificially severed membrane proteins can also yield functional, properly folded protein (4)(5)(6).…”

SDS-Facilitated In vitro Formation of a Transmembrane B-Type Cytochrome Is Mediated by Changes in Local pH

“…36 This value was somewhat unexpected, since the strength of a hydrogen-bond within a membrane environment having a low dielectric constant was expected to be much higher. 37 While addition of SDS to TM helix oligomers in DDM results in monomerization of the TM helix without altering the secondary structure, 21 the results of our study highlight an additional aspect that has to be taken into consideration when interpreting the results of SDS titration in mixed micelles, namely, SDS-induced changes in the local pH. To the best of our knowledge, there are no reports, aside from this work, documenting that intermediate concentrations of SDS can actually have a beneficial effect on cofactor binding or protein folding and assembly.…”

“…19,22,[32][33][34] Addition of SDS to a membrane protein dissolved in a mild detergent, such as DDM, may lead to loss of the native structure (for monomeric proteins such as bacteriorhodopsin) or result in dissociation of TM helices (for dimeric proteins such as glycophorin) without changing the secondary structure of a TM protein. 21 Assuming a linear relationship between the free energy of unfolding (ΔG unf ) and the SDS mole fraction, it is possible to extract ΔG unf values extrapolated to the absence of SDS. The data are often sufficiently accurate to discern changes in stability of less than 1 kcal/mol.…”

“…1), a micellar environment provides an opportunity to systematically vary the denaturing strength of the environment surrounding the membrane protein by formation of mixed micelles. In this approach, pioneered by Lau and Bowie 19 and used by other groups subsequently, [20][21][22] a TM protein is solubilized in a mild non-ionic detergent, typically n-dodecyl-β-maltoside (DDM), and addition of the anionic detergent SDS results in formation of mixed micelles coupled with dissociation of TM helices. Note that conformational changes probed by this method follow the second stage of the two-stage model, since individual helices are also formed in SDS micelles, although they may differ from native-state helices.…”

Interaction of a two-transmembrane-helix peptide with lipid bilayers and dodecyl sulfate micelles

“…Their results show that glycophorin has intact α-helices and extensive inter-helix side chain interactions in SDS. Recent studies of synthetic peptides in micelles have reached opposite conclusions about the effect of SDS on helix-helix interactions [4, 5]. Many spectroscopic changes have been observed when integral membrane proteins are transferred into SDS micelles.…”