Membrane fusion during secretion. A hypothesis based on electron microscope observation of Phytophthora Palmivora zoospores during encystment.

Silva, P Pinto da; Nogueira, M L

doi:10.1083/jcb.73.1.161

Cited by 151 publications

(39 citation statements)

References 30 publications

(32 reference statements)

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“…The fracture plane is deflected at the site of each particle and it is this deflection that morphologically determines the particle itself: i.e., the membrane particles are defined relative to, and in contradistinction to, the bilayer continuum of biomembranes. Although in every successfully investigated case integral membrane proteins (and, in consequence, their tightly associated lipids) were shown to be components of the membrane particles, the presence of integral proteins is not, in principle, a necessary condition; micellar subphases sequestered within the polar matrix of the bilayer can also appear, in freeze-fractured preparations, as "particles"-i.e., as local deviations of the fracture plane, albeit with a characteristic morphology (25,26). In many membranes, however, and particularly in specialized membranes (e.g., chloroplast grana) or membrane regions (e.g., gap junctions) interruptions of the bilayer continuum may account for most of the membrane area.…”

Section: Results Ultrastructurementioning

confidence: 99%

Fracture-label:O cytochemistry of freeze-fracture faces in the erythrocyte membrane.

Silva¹,

Parkison²,

Dwyer³

1981

Proc. Natl. Acad. Sci. U.S.A.

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A method-"fracture label"-is described for the cytochemical labeling of the membrane faces produced by freeze-fracture. Human erythrocytes embedded in a crosslinked matrix are frozen, fractured in liquid nitrogen, thawed, labeled, and cut into thin sections. Electron microscope observation of the fracture faces shows preferential partition of concanavalin A binding sites with the. inner half of the membrane. This signifies that, during freeze-fracture, binding sites are dragd from the outer surface across the outer ("exoplasmic") half of the membrane and retained on the protoplasmic fracture face (face P). The fracture process results in exposure of new. anionic-sites on face P. Fracture-label can be applied to the cytochemical characterization of the cellular components exposed. by freeze-fracture of isolated cells and tissues.Freeze-fracture splits membranes along their hydrophobic interior, following the juncture ofend groups provided by a membrane continuum with bilayer organization (1-4). Although fracture of the bilayer produces smooth faces, in all biological membranes these faces are interrupted by particulate components ("membrane intercalated particles" or "intramembranous particles") and, in most, by subtler rugosities ["subparticles" (5)]. Combined use ofimmunochemical and cytochemical techniques with freeze-etching methods, and freeze-fracture observation of reconstituted membrane preparations, demonstrate that, in the systems used, the particles represent the sites ofintegral transmembrane proteins (6-12). Because of the qualitative similarity offreeze-fracture images produced by all biological membranes, the particles are assumed to represent local structural asymmetries in the fracture process provoked by integral membrane.proteins and, possibly, their-associated lipids (3, 4). In the erythrocyte membrane the particles represent the site of the two main integral transmembrane proteins (glycophorin and band III component) which bear AB(H) antigens, influenza virus receptors, wheat germ agglutinin and concanavalin A (Con A) binding sites, as well as anionic sites (8)(9)(10)(11)(13)(14)(15).Although splitting of the bilayer continuum by freeze-fracture (and, in consequence, the partition of peripheral membrane proteins) is established, less is known about the fracture behavior of integral membrane proteins (3, 16)-in particular, their antigens and lectin binding sites at the surface (17). Most particles are generally associated with the inner membrane half (1, 2)-i. e., they are observed on the protoplasmic or P face (18). This may be the result ofa stochastic process or reflect individual differences of fracture behavior of the components in each particle or both. On face P the particles represent, at least in part, portions of integral proteins located at the outer (exoplasmic, E) membrane half. It is unknown whether the particles contain hydrophilic surface groups ofintegral proteins dragged, during fracture, from the outer surface. We have labeled freezefractured erythrocytes and repor...

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Section: Results Ultrastructurementioning

confidence: 99%

Fracture-label:O cytochemistry of freeze-fracture faces in the erythrocyte membrane.

Silva¹,

Parkison²,

Dwyer³

1981

Proc. Natl. Acad. Sci. U.S.A.

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“…Circular clearings of intramembranous particles have been described in various other fusional systems, such as frog neuromuscular junctions, pancreatic islet cells, and Phytophthora zoospores (10,42,46) . It has been argued that these maculae are artifactually produced by either glutaraldehyde or glycerol, for they were not seen in freeze-fracture images of quick-frozen mast cells (12) .…”

Section: Imp Clearingsmentioning

confidence: 99%

Modifications of anionic-lipid domains preceding membrane fusion in guinea pig sperm.

Bearer¹,

Friend²

1982

The Journal of Cell Biology

178

101

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The relationship between anionic-lipid concentration and the functional properties of plasma-membrane domains was explored using the guinea-pig sperm membrane as a model, with polymyxin B (PXB) as a probe. Areas of plasmalemma specialized for fusion during the acrosome reaction had a higher affinity for the probe than adjacent nonfusigenic regions. In addition, capacitation-a process preceding acrosome :plasma-membrane fusion-markedly enlarged the area susceptible to PXB binding over the acrosomal cap. Protease treatment mimicked capacitation by increasing the acrosome-reaction incidence as well as PXB binding, at enzyme concentrations not affecting the surface coat nor altering filipin/sterol localization . Both proteolytic digestion and capacitation failed to augment PXB-or filipin-affinity in nonfusigenic zones, such as the post-acrosomal segment, including its particle-free maculae. Incubation of sperm in capacitating medium supplemented with 32p_ labeled phosphate, followed by lipid extraction, thin-layer chromatography, and autoradiography, revealed a radioactive band comigràting with cardiolipin and phosphatidic acid . Vermiform protrusions elicited by PXB in the outer lamellae of card iolipin-phosphatidylcholine liposomes resembled those seen in fusional regions of sperm membrane . We conclude that (a) differing concentrations of anionic lipids are found in adjacent domains of the sperm plasma membrane ; (b) these domains mirror the functional regions of the membrane, with higher anionic-lipid concentrations localized over fusional zones; (c) the surface coat does not participate in the maintenance of such domains; (d) anionic-lipid synthesis may contribute to their formation; and (e) anionic-lipid concentrations increase as the membrane becomes fusionally competent, indicating that cellular modulation of lipid domains accompanies regulation of membrane function .That phospholipids mediate fusion in diverse biological or model membrane-systems has been advocated by a number of investigators. Particularly, workers in reproductive biology have shown that fertilization is not prevented by the treatment of eggs with proteolytic or carbohydrate-hydrolyzing enzymes which leave phospholipids intact (26) . Moreover, biophysicists have established that phospholipid vesicles can fuse, not only with each other (44) but with natural membranes (23,55) . Certain lipids have a greater potential for fusion than others. For example, liposomes composed solely of phosphatidylcholine (PC) resist merger for hours, yet vesicle membranes incorporating anionic lipids fuse readily upon the introduction of divalent cations (44) .The requirement for negatively charged lipids in the events of membrane :membrane fusion has been demonstrated in various systems-e.g., the entry of Semliki Forest virus into cells via the viral envelope-membrane union with the cell's lyso-604

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“…Initial freeze-fracture experiments [95][96][97] suggested that fusion could proceed only after clearance of the protein particles. It was assumed that regions free of intramembrane particles or at least relatively large exposed bilayer regions were necessary for actual fusion to occur.…”

Section: Vc Membrane Fusionmentioning

confidence: 99%

Lipidic intramembranous particles

Verkleij

1984

Biochimica et Biophysica Acta (BBA) - Reviews on Biomembranes

411

166

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Membrane fusion during secretion. A hypothesis based on electron microscope observation of Phytophthora Palmivora zoospores during encystment.

Cited by 151 publications

References 30 publications

Fracture-label:O cytochemistry of freeze-fracture faces in the erythrocyte membrane.

Fracture-label:O cytochemistry of freeze-fracture faces in the erythrocyte membrane.

Modifications of anionic-lipid domains preceding membrane fusion in guinea pig sperm.

Lipidic intramembranous particles

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