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

Cho WJ, Shin L, Ren G, Jena BP - J. Cell. Mol. Med. (2009)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, USA.

ABSTRACT
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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Negatively stained electron micrograph of isolated neuronal porosome protein complexes. Note the 12–17-nm complexes exhibiting a circular profile and having a central plug. Approximately 8 to 10 interconnected protein densities are observed at the rim of the structure, which are connected to a central element via spoke-like structures. At the centre of the structure, which corresponds to the porosome base, there are proteins, most likely SNAREs arranged in rings (yellow arrowhead). Bar = 5 nm. [15].
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fig03: Negatively stained electron micrograph of isolated neuronal porosome protein complexes. Note the 12–17-nm complexes exhibiting a circular profile and having a central plug. Approximately 8 to 10 interconnected protein densities are observed at the rim of the structure, which are connected to a central element via spoke-like structures. At the centre of the structure, which corresponds to the porosome base, there are proteins, most likely SNAREs arranged in rings (yellow arrowhead). Bar = 5 nm. [15].

Mentions: The ring complex at the base of neuronal porosome (Fig. 3) appears to possess a diameter almost half that of the t-/v-SNARE ring complexes formed when such 50–60 nm t-SNARE-vesicles and v-SNARE-vesicles meet. This can be explained, since the 12–17 nm in diameter cup-shaped neuronal porosome complex has a mere 3–4 nm in diameter base where 40–50 nm in diameter synaptic vesicle transiently docks and fuses to release neurotransmitters. This allows room for only one or two SNARE ring complexes at the neuronal porosome base, each ring composed of merely three SNARE pairs (Fig. 3 inset), and a central channel measuring just 1–1.5 nm in diameter. Unlike exocrine or neuroendocrine secretions, the 1–1.5 nm in diameter central channel would be adequate for neurotransmitter release as a result of the build-up of intravesicular pressure following synaptic vesicle swelling during neurotransmission [17, 18].


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

Cho WJ, Shin L, Ren G, Jena BP - J. Cell. Mol. Med. (2009)

Negatively stained electron micrograph of isolated neuronal porosome protein complexes. Note the 12–17-nm complexes exhibiting a circular profile and having a central plug. Approximately 8 to 10 interconnected protein densities are observed at the rim of the structure, which are connected to a central element via spoke-like structures. At the centre of the structure, which corresponds to the porosome base, there are proteins, most likely SNAREs arranged in rings (yellow arrowhead). Bar = 5 nm. [15].
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4496122&req=5

fig03: Negatively stained electron micrograph of isolated neuronal porosome protein complexes. Note the 12–17-nm complexes exhibiting a circular profile and having a central plug. Approximately 8 to 10 interconnected protein densities are observed at the rim of the structure, which are connected to a central element via spoke-like structures. At the centre of the structure, which corresponds to the porosome base, there are proteins, most likely SNAREs arranged in rings (yellow arrowhead). Bar = 5 nm. [15].
Mentions: The ring complex at the base of neuronal porosome (Fig. 3) appears to possess a diameter almost half that of the t-/v-SNARE ring complexes formed when such 50–60 nm t-SNARE-vesicles and v-SNARE-vesicles meet. This can be explained, since the 12–17 nm in diameter cup-shaped neuronal porosome complex has a mere 3–4 nm in diameter base where 40–50 nm in diameter synaptic vesicle transiently docks and fuses to release neurotransmitters. This allows room for only one or two SNARE ring complexes at the neuronal porosome base, each ring composed of merely three SNARE pairs (Fig. 3 inset), and a central channel measuring just 1–1.5 nm in diameter. Unlike exocrine or neuroendocrine secretions, the 1–1.5 nm in diameter central channel would be adequate for neurotransmitter release as a result of the build-up of intravesicular pressure following synaptic vesicle swelling during neurotransmission [17, 18].

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201, USA.

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus