Porosome: The Universal Secretory Machinery in Cells

Jena, Bhanu P.

doi:10.1002/0470007702.ch1

Cited by 7 publications

(11 citation statements)

References 42 publications

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“…Membrane cholesterol was shown to regulate the activation kinetics of the channel resulting in a shift in the activation curve, as well as to regulate channel trafficking (Hinzpeter et al, 2007). Identification of ClC-2 and ClC-3 channels as a part of the neuronal fusion pore, a process that requires cholesterol, suggests that cholesterol-sensitivity of these channels may affect pore formation (Cho et al, 2007; Jena, 2008). However, a specific functional link between the channels and cholesterol has not been established yet.…”

Section: 10 Cl− Channelsmentioning

confidence: 99%

Cholesterol and Ion Channels

Levitan

Fang

Rosenhouse‐Dantsker

et al. 2010

Subcellular Biochemistry

194

178

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A variety of ion channels, including members of all major ion channel families, have been shown to be regulated by changes in the level of membrane cholesterol and partition into cholesterol-rich membrane domains. In general, several types of cholesterol effects have been described. The most common effect is suppression of channel activity by an increase in membrane cholesterol, an effect that was described for several types of inwardly-rectifying K + channels, voltage-gated K + channels, Ca +2 sensitive K + channels, voltage-gated Na + channels, N-type voltage-gated Ca +2 channels and volume-regulated anion channels. In contrast, several types of ion channels, such as epithelial amiloride-sensitive Na + channels and Transient Receptor Potential channels, as well as some of the types of inwardly-rectifying and voltage-gated K + channels were shown to be inhibited by cholesterol depletion. Cholesterol was also shown to alter the kinetic properties and current-voltage dependence of several voltage-gated channels. Finally, maintaining membrane cholesterol level is required for coupling ion channels to signalling cascades. In terms of the mechanisms, three general mechanisms have been proposed: (i) specific interactions between cholesterol and the channel protein, (ii) changes in the physical properties of the membrane bilayer and (iii) maintaining the scaffolds for proteinprotein interactions. The goal of this review is to describe systematically the role of cholesterol in regulation of the major types of ion channels and to discuss these effects in the context of the models proposed. KeywordsIon channels; Cholesterol; Lipid rafts IntroductionDuring the last decade, a growing number of studies have demonstrated that the level of membrane cholesterol is a major regulator of ion channel function (reviewed by Maguy et al., 2006;Martens et al., 2004). It is also becoming increasingly clear that the impact of cholesterol on different types of ion channels is highly heterogeneous. The most common effect is cholesterol-induced decrease in channel activity that may include decrease in the open probability, unitary conductance and/or the number of active channels on the membrane. This effect was observed in several types of K + channels, voltage-gated Na + and Ca +2 channels, as well as in volume-regulated anion channels. However, there are also several types of ion channels, such as epithelial Na + channels (eNaC) and transient receptor potential (Trp) channels that are inhibited by the removal of membrane cholesterol. Finally, in some cases changes in membrane cholesterol affect biophysical properties of the channel such as the voltage dependence of channel activation or inactivation. Clearly, therefore, more than one mechanism has to be involved in cholesterol-induced regulation of different ion channels.

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Section: 10 Cl− Channelsmentioning

confidence: 99%

Cholesterol and Ion Channels

Levitan

Fang

Rosenhouse‐Dantsker

et al. 2010

Subcellular Biochemistry

194

178

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“…(G) Note the high correlation coefficient between vesicle diameter and size of the SNARE complex [8]. [16].…”

Section: Fig 1 Opposing Bilayers Containing T-and V-snares Respectimentioning

confidence: 99%

“…The top panel is a side view of two vesicles (one t-SNARE-reconstituted, and the other v-SNARE reconstituted) interacting to form a single t-/v-SNARE complex, leading progressively (from left to right) to the formation of the ring complex. The lower panel is a top view of the two interacting vesicles [16]. …”

Section: Introductionmentioning

confidence: 99%

Structure of membrane‐associated neuronal SNARE complex: implication in neurotransmitter release

Cho

Shin

Ren

et al. 2009

J Cellular Molecular Medi

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To enable fusion between biological membranes, t-SNAREs and v-SNARE present in opposing bilayers, interact and assemble in a circular configuration forming ring-complexes, which establish continuity between the opposing membranes, in presence of calcium ions. The size of a t-/v-SNARE ring complex is dictated by the curvature of the opposing membrane. Hence smaller vesicles form small SNARE-ring complexes, as opposed to large vesicles. Neuronal communication depends on the fusion of 40–50 nm in diameter membrane-bound synaptic vesicles containing neurotransmitters at the nerve terminal. At the presynaptic membrane, 12–17 nm in diameter cup-shaped neuronal porosomes are present where synaptic vesicles transiently dock and fuse. Studies demonstrate the presence of SNAREs at the porosome base. Atomic force microscopy (AFM), electron microscopy (EM), and electron density measurement studies demonstrate that at the porosome base, where synaptic vesicles dock and transiently fuse, proteins, possibly comprised of t-SNAREs, are found assembled in a ring conformation. To further determine the structure and arrangement of the neuronal t-/v-SNARE complex, 50 nm t-and v-SNARE proteoliposomes were mixed, allowing t-SNARE-vesicles to interact with v-SNARE vesicles, followed by detergent solubilization and imaging of the resultant t-/v-SNARE complexes formed using both AFM and EM. Our results demonstrate formation of 6–7 nm membrane-directed self-assembled t-/v-SNARE ring complexes, similar to, but twice as large as the ring structures present at the base of neuronal porosomes. The smaller SNARE ring at the porosome base may reflect the 3–4 nm base diameter, where 40–50 nm in diameter v-SNARE-associated synaptic vesicle transiently dock and fuse to release neurotransmitters.

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“…Until recently, it was commonly accepted that the final step in secretion is the total incorporation of secretory vesicle membrane into the cell plasma membrane leading to the release of intravesicular contents by diffusion, and the compensatory retrieval of excess membrane by endocytosis at a later time (Ichikawa, 1965;Ceccarelli et al, 1972;Dreifuss, 1975;Saras et al, 1981;Ryan et al, 1996;Valentijn et al, 1999;Zenisek et al, 2002;Heidelberger, 2001;Sudhof, 1995;Fischer von Mollard et al, 1994;Walch-Solimena et al, 1995). Studies within the past 20 years have finally revealed a completely different molecular mechanism of secretion and membrane fusion in cells Cho et al, 2002aCho et al, ,c,e, 2004Jena, 2002Jena, , 2004Jena, , 2005Jena, , 2007Jena, , 2008Jena, , 2009aJena, ,b, 2010Jena et al, 1997Jena et al, , 2003Jeremic et al, 2003Jeremic et al, , 2004aJeremic et al, ,b, 2005Jeremic et al, , 2006Clary et al, 1990;Söllner et al, 1993;Rothman and Söllner, 1997;Weber et al, 1988;Craciun, 2004;Jeftinija, 2006;Leabu, 2006;Anderson, 2006a,b). Monck and Fernandez (1996) suggested the existence of fusion pore at the cell plasma membrane, which became continuous with the secretory vesicle membrane after stimulation of secretion.…”

Section: Introductionmentioning

confidence: 99%