Abstract
Lipids and block copolymers can individually self-assemble into vesicles, each with their own particular benefits and limitations. Combining polymers with lipids allows for further optimisation of the vesicle membranes for bionanotechnology applications. Here, POPC lipid is mixed with poly(1,2-butadiene-block-ethylene oxide) of two different molecular weights (PBd22-PEO14, Mr = 1800 g mol-1 and PBd12-PEO11, Mr = 1150 g mol-1) in order to investigate how increasing the polymer fraction affects membrane mixing, hydration and fluidity. Intensity contributions of fluorescently labelled lipid and polymer within mixed GUV membranes confirm membrane homogeneity within the hybrids. General polarisation measurements of Laurdan in GUVs showed little change in membrane hydration as polymer fraction is increased, which suggests good structural compatibility between lipids and polymers that gives rise to well-mixed vesicles. Membrane fluidity in hybrid GUVs was found to decrease non-linearly with increasing polymer fraction. However, the diffusion coefficients for the fluorescent polymer in hybrid membranes did not change significantly with increasing polymer content. While increasing the polymer fraction does reduce the movement of lipids through a polymer-rich matrix, insignificant difference in diffusion coefficients of the polymer suggests that its diffusion is minimally affected by increasing lipid composition in the range studied. These results lay further foundations for the wider development of hybrid vesicles with controlled properties for advanced biotechnologies.
Highlights
Lipids and block copolymers can individually self-assemble into vesicles, each with their own particular benefits and limitations
Besides enhanced durability of protein function, block copolymers have been shown to enhance membrane protein folding into hybrid vesicles: up to 25 mol% of PBd22–PEO14 or PBd12–PEO9 in DOPC hybrid vesicles enhanced MScL protein folding during cell-free expression.[20]
giant unilamellar vesicles (GUVs) composed of mixtures of the lipid POPC with either PBd22–PEO14 or PBd12–PEO11 were created by using the electroformation method
Summary
Lipids and block copolymers can individually self-assemble into vesicles, each with their own particular benefits and limitations. While increasing the polymer fraction does reduce the movement of lipids through a polymer-rich matrix, insignificant difference in diffusion coefficients of the polymer suggests that its diffusion is minimally affected by increasing lipid composition in the range studied These results lay further foundations for the wider development of hybrid vesicles with controlled properties for advanced biotechnologies. PBd22–PEO14 blended with E.coli extracted lipids has been used to successfully reconstitute two ATP binding cassette membrane proteins, P-gp or NaAtm1.9 Combinations of membrane proteins have been successfully reconstituted into PBd-b-PEO hybrid vesicles: F0 À F1 ATP synthase and bacteriorhodopsin in 50 mol% PBd22–PEO14/ POPC hybrid vesicles retained 450% of their activity after 42 days.[10] Besides enhanced durability of protein function, block copolymers have been shown to enhance membrane protein folding into hybrid vesicles: up to 25 mol% of PBd22–PEO14 or PBd12–PEO9 in DOPC hybrid vesicles enhanced MScL protein folding during cell-free expression.[20] improved understanding of the physicochemical properties of these hybrid membranes should further enhance their optimisation for membrane protein biotechnology
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