Detergents might affect membrane protein structures by promoting intramolecular interactions that are different from those found in native membrane bilayers, and fine-tuning detergent properties can be crucial for obtaining structural information of intact and functional transmembrane proteins. To systematically investigate the influence of the detergent concentration and acyl-chain length on the stability of a transmembrane protein structure, the stability of the human glycophorin A transmembrane helix dimer has been analyzed in lyso-phosphatidylcholine micelles of different acyl-chain length. While our results indicate that the transmembrane protein is destabilized in detergents with increasing chain-length, the diameter of the hydrophobic micelle core was found to be less crucial. Thus, hydrophobic mismatch appears to be less important in detergent micelles than in lipid bilayers and individual detergent molecules appear to be able to stretch within a micelle to match the hydrophobic thickness of the peptide. However, the stability of the GpA TM helix dimer linearly depends on the aggregation number of the lyso-PC detergents, indicating that not only is the chemistry of the detergent headgroup and acyl-chain region central for classifying a detergent as harsh or mild, but the detergent aggregation number might also be important.

The charge state of dielectric surfaces in aqueous environments is of fundamental and technological importance. Here, we study the influence of dissolved molecular CO2 on the charging of three chemically different surfaces (SiO2, Polystyrene, Perfluorooctadecyltrichlorosilane). We determine their charge state from electrokinetic experiments. We compare an ideal, CO2-free reference system to a system equilibrated against ambient CO2 conditions. In the reference system, the salt-dependent decrease of the magnitudes of ζ-potentials follows the expectations for a constant charge scenario. In the presence of CO2, the starting potential is lower by some 50%. The following salt-dependent decrease is weakened for SiO2 and inverted for the organic surfaces. We show that screening and pH-driven charge regulation alone cannot explain the observed effects. As an additional cause, we tentatively suggest dielectric regulation of surface charges due to a diffusively adsorbed thin layer of molecular CO2. The formation of such a dynamic layer, even at the hydrophilic and partially ionized silica surfaces, is supported by a minimal theoretical model and results from molecular simulations.