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Issue 23, 2017
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Cations induce shape remodeling of negatively charged phospholipid membranes

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Abstract

The divalent cation Ca2+ is a key component in many cell signaling and membrane trafficking pathways. Ca2+ signal transduction commonly occurs through interaction with protein partners. However, in this study we show a novel mechanism by which Ca2+ may impact membrane structure. We find an asymmetric concentration of Ca2+ across the membrane triggers deformation of membranes containing negatively charged lipids such as phosphatidylserine (PS) and phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2). Membrane invaginations in vesicles were observed forming away from the leaflet with higher Ca2+ concentration, showing that Ca2+ induces negative curvature. We hypothesize that the negative curvature is produced by Ca2+-induced clustering of PS and PI(4,5)P2. In support of this notion, we find that Ca2+-induced membrane deformation is stronger for membranes containing PI(4,5)P2, which is known to more readily cluster in the presence of Ca2+. The observed Ca2+-induced membrane deformation is strongly influenced by Na+ ions. A high symmetric [Na+] across the membrane reduces Ca2+ binding by electrostatic shielding, inhibiting Ca2+-induced membrane deformation. An asymmetric [Na+] across the membrane, however, can either oppose or support Ca2+-induced deformation, depending on the direction of the gradient in [Na+]. At a sufficiently high asymmetric Na+ concentration it can impact membrane structure in the absence of Ca2+. We propose that Ca2+ works in concert with curvature generating proteins to modulate membrane curvature and shape transitions. This novel structural impact of Ca2+ could be important for Ca2+-dependent cellular processes that involve the creation of membrane curvature, including exocytosis, invadopodia, and cell motility.

Graphical abstract: Cations induce shape remodeling of negatively charged phospholipid membranes

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Publication details

The article was received on 01 Feb 2017, accepted on 26 May 2017 and first published on 26 May 2017


Article type: Paper
DOI: 10.1039/C7CP00718C
Citation: Phys. Chem. Chem. Phys., 2017,19, 15285-15295
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    Cations induce shape remodeling of negatively charged phospholipid membranes

    Z. T. Graber, Z. Shi and T. Baumgart, Phys. Chem. Chem. Phys., 2017, 19, 15285
    DOI: 10.1039/C7CP00718C

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