The asymmetric plasma membrane—A composite material combining different functionalities?

One persistent puzzle in the life sciences is the asymmetric lipid composition of the cellular plasma membrane: while the exoplasmic leaflet is enriched in lipids carrying predominantly saturated fatty acids, the cytoplasmic leaflet hosts preferentially lipids with (poly‐)unsaturated fatty acids. Gi...

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Bibliographic Details
Published in:BioEssays 2023-12, Vol.45 (12), p.n/a
Main Authors: Schütz, Gerhard J., Pabst, Georg
Format: Article
Language:English
Subjects:
diffusion
fluidity
lipids
membrane asymmetry
permeability
plasma membrane
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Summary:One persistent puzzle in the life sciences is the asymmetric lipid composition of the cellular plasma membrane: while the exoplasmic leaflet is enriched in lipids carrying predominantly saturated fatty acids, the cytoplasmic leaflet hosts preferentially lipids with (poly‐)unsaturated fatty acids. Given the high energy requirements necessary for cells to maintain this asymmetry, the question naturally arises regarding its inherent benefits. In this paper, we propose asymmetry to represent a potential solution for harmonizing two conflicting requirements for the plasma membrane: first, the need to build a barrier for the uncontrolled influx or efflux of substances; and second, the need to form a fluid and dynamic two‐dimensional substrate for signaling processes. We hence view here the plasma membrane as a composite material, where the exoplasmic leaflet is mainly responsible for the functional integrity of the barrier and the cytoplasmic leaflet for fluidity. We reinforce the validity of the proposed mechanism by presenting quantitative data from the literature, along with multiple examples that bolster our model. The lipid composition of the two plasma membrane leaflets is highly asymmetric. Here we speculate whether lipid asymmetry reflects nature's need for harmonizing conflicting demands. We assign two plasma membrane functions to the two leaflets: the outer leaflet provides resistance to hydrophilic substances, and the inner leaflet fluidity to signaling molecules.
ISSN:0265-9247
1521-1878
DOI:10.1002/bies.202300116