The effect of salt and pH on block liposomes studied by cryogenic transmission electron microscopy

Alexandra Zidovska, Kai K. Ewert, Joel Quispe, Bridget Carragher, Clinton S. Potter, Cyrus R. Safinya

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Recently, we have reported the discovery of block liposomes (BLs), a new class of liquid (chain-melted) vesicles, formed in mixtures of the curvature-stabilizing hexadecavalent cationic lipid MVLBG2, the neutral lipid 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC), and water with no added salt. BLs consist of connected spheres, pears, tubes, or rods. Unlike in typical liposome systems, where spherical vesicles, tubular vesicles, and cylindrical micelles are separated on the macroscopic scale, shapes remain connected and are separated only on the nanometer scale within a single BL. Here, we report structural studies of the effect of salt and pH on the BL phase, carried out using differential interference contrast microscopy (DIC) and cryogenic transmission electron microscopy (cryo-TEM). Addition of salt screens the electrostatic interactions; in low-salt conditions, partial screening of electrostatic interactions leads to a shape transition from BLs to bilamellar vesicles, while in the high-salt regime, a shape transition from BLs to liposomes with spherical morphologies occurs. This demonstrates that strong electrostatic interactions are essential for BL formation. Understanding the control of liposome shape evolution is of high interest because such shape changes play an important role in many intracellular processes such as endocytosis, endoplasmatic reticulum-associated vesiculation, vesicle recycling and signaling.

    Original languageEnglish (US)
    Pages (from-to)1869-1876
    Number of pages8
    JournalBiochimica et Biophysica Acta - Biomembranes
    Volume1788
    Issue number9
    DOIs
    StatePublished - Sep 2009

    Keywords

    • Block liposome
    • Charged membrane
    • Cryo-TEM
    • Curvature stabilization

    ASJC Scopus subject areas

    • Biophysics
    • Biochemistry
    • Cell Biology

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