Membrane Deformation Switching of an Endocytic Protein by Membrane Electrostatic Charge and Packing

Regulation of caveolae through cholesterol-depletion dependent tubulation by PACSIN2/Syndapin II

10.1101/2020.03.25.008854 ◽

2020 ◽

Author(s):

Aini Gusmira Amir ◽

Kazuhiro Takemura ◽

Kyoko Hanawa-Suetsugu ◽

Kayoko Oono-Yakura ◽

Kazuma Yasuhara ◽

...

Keyword(s):

Plasma Membrane ◽

Lipid Composition ◽

Electrostatic Charge ◽

Cholesterol Depletion ◽

Membrane Deformation ◽

Bar Domain ◽

Caveolin 1 ◽

Membrane Tubulation ◽

Shaping Ability

AbstractThe membrane shaping ability of PACSIN2 via its FCH-BAR (F-BAR) domain has been shown to be essential for caveolar morphogenesis, presumably through the shaping of the caveolar neck. Caveolar membrane contains abundant levels of cholesterol. However, the role of cholesterol in PACSIN2-mediated membrane deformation remains unclear. We show that the binding of PACSIN2 to the membrane could be negatively regulated by the amount of cholesterol in the membrane. We prepared a reconstituted membrane based on the lipid composition of caveolae. The reconstituted membrane with cholesterol had a weaker affinity to the F-BAR domain of PACSIN2 than the membrane without cholesterol, presumably due to a decrease in electrostatic charge density. Consistently, the acute depletion of cholesterol from the plasma membrane resulted in the appearance of PACSIN2-localized tubules with caveolin-1 at their tips, suggesting that the presence of cholesterol inhibited the prominent membrane tubulation by PACSIN2. The tubules induced by PACSIN2 were suggested to be an intermediate of caveolae endocytosis. Consistently, the removal of caveolae from the plasma membrane upon cholesterol depletion was diminished in the cells deficient in PACSIN2. These data suggested that PACSIN2 mediated the caveolae internalization dependently on the amount of cholesterol at the plasma membrane, providing a possible mechanism for the cholesterol-dependent regulation of caveolae.

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Problems with oxygen analysis in the system MgO-Al2O3-SiO2 with the electron microprobe

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100132753 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1624-1625

Author(s):

Michel Fialin ◽

Guy Rémond

Keyword(s):

Transition Metal ◽

Metal Oxides ◽

Transition Metal Oxides ◽

Electrostatic Charge ◽

Carbon Layer ◽

Sample Holder ◽

Rock Matrix ◽

Electrical Discharges ◽

Thin Carbon ◽

Beam Instabilities

Oxygen-bearing minerals are generally strong insulators (e.g. silicates), or if not (e.g. transition metal oxides), they are included within a rock matrix which electrically isolates them from the sample holder contacts. In this respect, a thin carbon layer (150 Å in our laboratory) is evaporated on the sections in order to restore the conductivity. For silicates, overestimated oxygen concentrations are usually noted when transition metal oxides are used as standards. These trends corroborate the results of Bastin and Heijligers on MgO, Al2O3 and SiO2. According to our experiments, these errors are independent of the accelerating voltage used (fig.l).Owing to the low density of preexisting defects within the Al2O3 single-crystal, no significant charge buildup occurs under irradiation at low accelerating voltage (< 10keV). As a consequence, neither beam instabilities, due to electrical discharges within the excited volume, nor losses of energy for beam electrons before striking the sample, due to the presence of the electrostatic charge-induced potential, are noted : measurements from both coated and uncoated samples give comparable results which demonstrates that the carbon coating is not the cause of the observed errors.

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Lectin-Induced RBC Agglutination: Chemical vs. Cryofixation

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600002920 ◽

1980 ◽

Vol 38 ◽

pp. 664-665

Author(s):

Dean A. Handley ◽

Lanping A. Sung ◽

Shu Chien

Keyword(s):

Lectin Binding ◽

Freeze Substitution ◽

Electrostatic Charge ◽

Geometric Parameters ◽

Comparative Approach ◽

Chemical Fixation ◽

Cell Surfaces ◽

Minimal Cell ◽

Membrane Stiffness ◽

Cell Contour

RBC agglutination by lectins represents an interactive balance between the attractive (bridging) force due to lectin binding on cell surfaces and disaggregating forces, such as membrane stiffness and electrostatic charge repulsion (1). During agglutination, critical geometric parameters of cell contour and intercellular distance reflect the magnitude of these interactive forces and the size of the bridging macromolecule (2). Valid ultrastructural measurements of these geometric parameters from agglutinated RBC's require preservation with minimal cell distortion. As chemical fixation may adversely influence RBC geometric properties (3), we used chemical fixation and cryofixation (rapid freezing followed by freeze-substitution) as a comparative approach to examine these parameters from RBC agglutinated with Ulex I lectin.

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