Membranes linked by trans-SNARE complexes require lipids prone to non-bilayer structure for progression to fusion

Zick, Michael; Stroupe, Christopher; Orr, Amy; Douville, Deborah; Wickner, William

doi:10.7554/elife.01879

Cited by 84 publications

(97 citation statements)

References 57 publications

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“…Even with trans-SNARE pairing linking apposed membranes, the rate of fusion is strongly enhanced by the presence of a tether, whether the physiological Ypt7-HOPS tether or a synthetic tether such as polyethylene glycol (17). In either case, small-headgroup lipids, which lower the energy for membrane transitions through nonbilayer intermediates, are required for meaningful fusion rates (25). We now report that Sec17 can dramatically accelerate fusion once trans-SNARE pairs have assembled.…”

Section: Discussionmentioning

confidence: 87%

“…To optimize the stimulation by Sec17, we varied the lipid composition of the proteoliposomes. We have recently reported that acidic lipids (24) and small-headgroup lipids (25) Proteoliposomes of only PC and PS were less active than those of vacuolar lipid composition but were strongly stimulated by the addition of Sec17 (Fig. 2B) in the absence of Sec18 or ATP.…”

Section: Resultsmentioning

confidence: 99%

“…It has been suggested that fusion is largely regulated through controlling trans-SNARE pairing (26). However, tethering factors and nonbilayerprone lipids are essential for fusion beyond modulating the level of trans-SNARE pairing (20,25). We therefore assayed both fusion and trans-SNARE pairing between proteoliposomes bearing Ypt7-GTP and the R-SNARE Nyv1 and those with Ypt7-GTP and the Qa-SNARE Vam3.…”

Section: Resultsmentioning

confidence: 99%

“…Several factors can contribute to lowering the energy barrier for two apposed membranes to rearrange their bilayers for fusion: (i) the physical force of membrane deformation deriving from trans-SNARE complexes forming continuous α-helices between their SNARE and transmembrane domains (42) [the initial concept that the energy for fusion derives entirely from forming a continuous α-helix between SNARE and transmembrane domains has been questioned by observations that transmembrane domains can be replaced by lipidic anchors for yeast vacuole fusion (43) or neuronal fusion (44)]; (ii) the docking of membranes in close proximity (45,46); (iii) the membrane bending that surrounds an extended region of membrane contact, driven by tethers (47); (iv) the enrichment of small headgroup lipids that can more readily fit into the nonbilayer lipidic structures of hemifusion and fusion intermediate states (25,34); and (v) localized (e.g., trans-SNARE-associated) additional proteins or other factors that can bind to lipids or insert into membranes to promote nonbilayer transitions. The latter includes Ca 2+ -triggered insertion of synaptotagmin at the neuronal synapse (48) and Sec17 for intracellular fusion.…”

Section: Discussionmentioning

confidence: 99%

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Sec17 can trigger fusion of trans -SNARE paired membranes without Sec18

Zick

Orr

Schwartz³

et al. 2015

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

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120

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Sec17 [soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein; α-SNAP] and Sec18 (NSF) perform ATP-dependent disassembly of cis-SNARE complexes, liberating SNAREs for subsequent assembly of trans-complexes for fusion. A mutant of Sec17, with limited ability to stimulate Sec18, still strongly enhanced fusion when ample Sec18 was supplied, suggesting that Sec17 has additional functions. We used fusion reactions where the four SNAREs were initially separate, thus requiring no disassembly by Sec18. With proteoliposomes bearing asymmetrically disposed SNAREs, tethering and trans-SNARE pairing allowed slow fusion. Addition of Sec17 did not affect the levels of trans-SNARE complex but triggered sudden fusion of trans-SNARE paired proteoliposomes. Sec18 did not substitute for Sec17 in triggering fusion, but ADP-or ATPγS-bound Sec18 enhanced this Sec17 function. The extent of the Sec17 effect varied with the lipid headgroup and fatty acyl composition of the proteoliposomes. Two mutants further distinguished the two Sec17 functions: Sec17 L291A,L292A did not stimulate Sec18 to disassemble cis-SNARE complex but triggered the fusion of trans-SNARE paired membranes. Sec17 F21S,M22S , with diminished apolar character to its hydrophobic loop, fully supported Sec18-mediated SNARE complex disassembly but had lost the capacity to stimulate the fusion of trans-SNARE paired membranes. To model the interactions of SNARE-bound Sec17 with membranes, we show that Sec17, but not Sec17 F21S,M22S , interacted synergistically with the soluble SNARE domains to enable their stable association with liposomes. We propose a model in which Sec17 binds to trans-SNARE complexes, oligomerizes, and inserts apolar loops into the apposed membranes, locally disturbing the lipid bilayer and thereby lowering the energy barrier for fusion.I ntracellular vesicular traffic between organelles is the basis of cell growth, hormone secretion, and neurotransmission. At each step of exocytic and endocytic trafficking, membranes dock and fuse, mixing their lipids and luminal contents while keeping them separate from the cytosol. Families of proteins, conserved from yeast to humans, mediate docking and fusion. Fusion requires Rab family GTPases and "effector" proteins that bind to a Rab in its active, GTP-bound state (1). Among the effectors are large, organelle-specific tethering complexes. Fusion requires SNARE proteins and their chaperones. SNAREs (2) are proteins that can "snare" (bind to) each other, in cis (when anchored to the same membrane) or in trans (when anchored to apposed, tethered membranes). SNAREs have a conserved "SNARE domain" with a characteristic heptad repeat. SNAREs are categorized as R-SNAREs if they have a central arginyl residue, or Qa-, Qb-, or Qc-SNAREs with a central glutamyl residue (3). SNAREs form RQaQbQc quaternary cis-or trans-SNARE complexes, which bind SNARE chaperones, including the Sec1/Munc18 family of SNARE binding proteins, and Sec18/NSF (N-ethylmaleimidesensitive factor), an AAA family ATPase that drives SNARE c...

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Section: Discussionmentioning

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Sec17 can trigger fusion of trans -SNARE paired membranes without Sec18

Zick

Orr

Schwartz³

et al. 2015

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

Self Cite

120

View full text Add to dashboard Cite

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“…1E). Although we cannot rule out other mechanisms of lipid transfer between cells, such as asymmetric lipid transfer or transient membrane rupture followed by reannealing (32), the extensive lipid mixing most likely reflects a deficit of the GPI-linked SNARE complexes in destabilizing the lipid bilayers and opening a fusion pore. If lipid-anchored STX11 mainly promotes incomplete fusion, how can it be essential for degranulation and cell-mediated cytotoxicity in CTLs and NK cells?…”

Section: Resultsmentioning

confidence: 99%

SM protein Munc18-2 facilitates transition of Syntaxin 11-mediated lipid mixing to complete fusion for T-lymphocyte cytotoxicity

Spessott

Sanmillan

McCormick

et al. 2017

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

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The atypical lipid-anchored Syntaxin 11 (STX11) and its binding partner, the Sec/Munc (SM) protein Munc18-2, facilitate cytolytic granule release by cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. Patients carrying mutations in these genes develop familial hemophagocytic lymphohistiocytosis, a primary immunodeficiency characterized by impaired lytic granule exocytosis. However, whether a SNARE such as STX11, which lacks a transmembrane domain, can support membrane fusion in vivo is uncertain, as is the precise role of Munc18-2 during lytic granule exocytosis. Here, using a reconstituted "flipped" cell-cell fusion assay, we show that lipidanchored STX11 and its cognate SNARE proteins mainly support exchange of lipids but not cytoplasmic content between cells, resembling hemifusion. Strikingly, complete fusion is stimulated by addition of wild-type Munc18-2 to the assay, but not of Munc18-2 mutants with abnormal STX11 binding. Our data reveal that Munc18-2 is not just a chaperone of STX11 but also directly contributes to complete membrane merging by promoting SNARE complex assembly. These results further support the concept that SM proteins in general are part of the core fusion machinery. This fusion mechanism likely contributes to other cell-type-specific exocytic processes such as platelet secretion.SNARE | Syntaxin 11 | Munc18-2 | CTL | SM protein

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Metabolism and functions of docosahexaenoic acid‐containing membrane glycerophospholipids

et al. 2017

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Omega‐3 (ω‐3) fatty acids (FAs) such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are known to have important roles in human health and disease. Besides being utilized as fuel, ω‐3 FAs have specific functions based on their structural characteristics. These functions include serving as ligands for several receptors, precursors of lipid mediators, and components of membrane glycerophospholipids (GPLs). Since ω‐3 FAs (especially DHA) are highly flexible, the levels of DHA in GPLs may affect membrane biophysical properties such as fluidity, flexibility, and thickness. Here, we summarize some of the cellular mechanisms for incorporating DHA into membrane GPLs and propose biological effects and functions of DHA‐containing membranes of several cell and tissue types.

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Membranes linked by trans-SNARE complexes require lipids prone to non-bilayer structure for progression to fusion

Cited by 84 publications

References 57 publications

Sec17 can trigger fusion of trans -SNARE paired membranes without Sec18

Sec17 can trigger fusion of trans -SNARE paired membranes without Sec18

SM protein Munc18-2 facilitates transition of Syntaxin 11-mediated lipid mixing to complete fusion for T-lymphocyte cytotoxicity

Metabolism and functions of docosahexaenoic acid‐containing membrane glycerophospholipids

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