Morphological Changes in Liposomes Caused by Polymerization of Encapsulated Actin and Spontaneous Formation of Actin Bundles

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 89; no. 23; pp. 11547 - 11551
• Main Authors: Miyata, Hidetake, Hotani, Hirokazu
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 01.12.1992; National Acad Sciences; National Academy of Sciences
• Subjects: actin; Actin Cytoskeleton - ultrastructure; Actins; Actins - physiology; Actins - ultrastructure; Animals; Artificial membranes and reconstituted systems; Biological and medical sciences; Birefringence; Cell Size; Cell-Free System; Cellular biology; Fluorescence; Fundamental and applied biological sciences. Psychology; Geometric shapes; In Vitro Techniques; Light; Lipids; Liposomes; Macromolecular Substances; Membrane physicochemistry; Microfilaments; Microscopy; Microtubules; Molecular biophysics; Physics; Polymerization; Polymers; Rabbits; Scattering, Radiation; Encapsulation; Optical microscopy; Filament; Stabilization; Morphology; Contractile protein; Actins; Liposome; Polymerization; Artificial membrane; Striated muscle
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.89.23.11547

Spherical giant liposomes that had encapsulated skeletal-muscle G-actin were made by swelling a dried lipid mixture of dimyristoyl phosphatidylcholine/cardiolipin, 1:1 (wt/wt), in a solution of G-actin/CaCl2at 0⚬C. Polymerization of the encapsulated G-actin into actin filaments was achieved by raising the temperature to 30⚬C. We observed the subsequent shape changes of the liposomes by dark-field and differential interference-contrast light microscopy. After ≈ 40 min, which was required for completion of actin polymerization, two shapes of liposome were evident: dumbbell and disk. Elongation of the dumbbell-shaped liposomes was concomitant with actin polymerization. Polarization microscopy showed that actin filaments formed thick bundles in the liposomes and that these filaments lay contiguous to the periphery of the liposome. Localization of actin filaments in the liposomes was confirmed by observation of rhodamine phalloidin-conjugated actin filaments by fluorescence microscopy. Both dumbbell-and disk-shaped liposomes were rigid and kept their shapes as far as actin filaments were stabilized. In contrast, liposomes containing bovine serum albumin were fragile, and their shapes continually fluctuated from Brownian motion, indicating that the actin bundles served as mechanical support for the liposome shapes.