Dataset Information

Detergent-phospholipid mixed micelles with a crystalline phospholipid core.

ABSTRACT: An unusual micelle was discovered in mixtures of the nonionic detergent octaethyleneglycol-mono-n-dodecylether with disaturated phospholipids such as 1,2-dimyristoyl-sn-glycero-3-phosphocholine or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine in water. These mixtures undergo a structural transition upon cooling through the chain-melting temperatures of the respective phospholipids, resulting in the formation of mixed micelles. Structural features of the micellar particles were studied here by synchrotron x-ray scattering. The translucent micellar solutions showed characteristic wide-angle reflections that were attributed to ordered hydrocarbon chains, whereas the absence of small-angle x-ray reflections indicated that there is no long-range order in these mixtures. The presence of ordered phospholipid acyl chains was confirmed by differential scanning calorimetry and isothermal titration calorimetry. The endothermic differential scanning calorimetry signals observed in the up-scan mode were tentatively ascribed to chain melting and mixing of the components. Isothermal titration of the mixed-micellar solutions into an excess of the detergent octaethyleneglycol-mono-n-dodecylether resulted in sudden uptake of the latent heat by the gel-state phospholipids. The heat uptake per mol of phospholipid decreased with increasing detergent/phospholipid molar ratio. A simple geometric model is presented assuming that the dominating particle species in the mixtures is a discoidal phospholipid aggregate with ordered acyl chains, surrounded by a toroidal detergent hoop. The model implies that the fraction of ordered phospholipid chains decreases with increasing detergent/phospholipid molar ratio, in agreement with the calorimetric results and high-resolution NMR spectroscopy.

SUBMITTER: Funari SS

PROVIDER: S-EPMC55352 | biostudies-literature | 2001 Jul

REPOSITORIES: biostudies-literature

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Detergent-phospholipid mixed micelles with a crystalline phospholipid core.

Funari S S SS Nuscher B B Rapp G G Beyer K K

Proceedings of the National Academy of Sciences of the United States of America 20010701 16

An unusual micelle was discovered in mixtures of the nonionic detergent octaethyleneglycol-mono-n-dodecylether with disaturated phospholipids such as 1,2-dimyristoyl-sn-glycero-3-phosphocholine or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine in water. These mixtures undergo a structural transition upon cooling through the chain-melting temperatures of the respective phospholipids, resulting in the formation of mixed micelles. Structural features of the micellar particles were studied here by sync ...[more]

PMID: 11481465

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Project description:Membrane proteins are largely dependent for their function on the phospholipids present in their immediate environment, and when they are solubilized by detergent for further study, residual phospholipids are critical, too. Here, brominated phosphatidylcholine, a phospholipid which behaves as an unsaturated phosphatidylcholine, was used to reveal the kinetics of phospholipid exchange or transfer from detergent mixed micelles to the environment of a detergent-solubilized membrane protein, the paradigmatic P-type ATPase SERCA1a, in which Trp residues can experience fluorescence quenching by bromine atoms present on phospholipid alkyl chains in their immediate environment. Using dodecylmaltoside as the detergent, exchange of (brominated) phospholipid was found to be much slower than exchange of detergent under the same conditions, and also much slower than membrane solubilization, the latter being evidenced by light scattering changes. The kinetics of this exchange was strongly dependent on temperature. It was also dependent on the total concentration of the mixed micelles, revealing the major role for such exchange of the collision of detergent micelles with the detergent-solubilized protein. Back-transfer of the brominated phospholipid from the solubilized protein to the detergent micelle was much faster if lipid-free DDM micelles instead of mixed micelles were added for triggering dissociation of brominated phosphatidylcholine from the solubilized protein, or in the additional presence of C12E8 detergent during exchange, also emphasizing the role of the chemical nature of the micelle/protein interface. This protocol using brominated lipids appears to be valuable for revealing the possibly slow kinetics of phospholipid transfer to or from detergent-solubilized membrane proteins. Independently, continuous recording of the activity of the protein can also be used in some cases to correlate changes in activity with the exchange of a specific phospholipid, as shown here by using the Drs2p/Cdc50p complex, a lipid flippase with specific binding sites for lipids.

Dataset Information

Detergent-phospholipid mixed micelles with a crystalline phospholipid core.

Publications

Detergent-phospholipid mixed micelles with a crystalline phospholipid core.

Similar Datasets

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