#vesicle fusion

Protein Sorting and Trafficking

Which of these regulates vesicle targeting and fusion?

Accurate membrane flow despite overlapping SNARE compatibility requires additional targeting layer beyond SNARE pairing. Rab small GTPases provide master regulation representing largest Ras superfamily with over 70 members humans each localized via C-terminal hypervariable domain plus geranylgeranyl modifications added by Rab geranylgeranyl transferase and REP. Localized activation by cognate GEFs DENN, TRAPP, Mon1-Ccz1 converts GDP to GTP exposing switch regions binding diverse effectors including long coiled-coil tethers golgin-84, GM130, p115 bridging distances, multisubunit complexes HOPS,

Ref: Stenmark, Nat Rev Mol Cell Biol: Rab GTPases coordinate vesicle targeting and fusion.

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Protein Sorting and Trafficking

What is the function of SNAP-25 in vesicle fusion?

Assembly of heteromeric SNARE core provides mechanical work for fusion in neurons, endocrine cells and constitutive secretion. Proteins classified into Q-SNAREs supplying glutamine at central zero ionic layer and R-SNAREs supplying arginine. Target plasma membrane harbors two Q proteins: syntaxin1 integral with single Q helix preceded by Habc regulatory domain clamped by Munc18 and SNAP-25 peripheral anchored via palmitoylated linker contributing two Q helices lacking transmembrane domain together contributing three Q motifs collectively t-SNARE. Vesicle membrane supplies R protein synaptobrev

Ref: Jahn & Scheller, Nat Rev Mol Cell Biol: SNAP-25 as Qbc t-SNARE in fusion.

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Protein Sorting and Trafficking

Which protein is responsible for recycling SNARE complexes for reuse?

Maintenance of available fusion-competent SNAREs requires constant recycling machinery whose failure halts secretion rapidly. After vesicle fusion, v- and t-SNAREs intertwined as cis complex on acceptor membrane representing low-energy product. Soluble alpha-SNAP 35 kDa oligomerizes along complex as three to four copies per bundle recognizing acidic surface patches. Hexameric NSF ATPase binds SNAP coat via N-domains forming 20S particle originally observed in detergent extracts. Upon ATP hydrolysis D1 ring undergoes large movements pulling SNAREs through central pore with mechanical force unfo

Ref: Alberts et al., MBC Chapter 13: NSF recycling of SNARE complexes for multiple rounds.

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Protein Sorting and Trafficking

What triggers the disassembly of SNARE complexes after membrane fusion?

Cis-SNARE complexes formed post-fusion are extremely stable four-helix bundles with melting temperature above 90 Celsius requiring energy for recycling. Disassembly machinery uses ATP. Hexameric AAA+ ATPase NSF N-ethylmaleimide sensitive factor assembles as ring with two stacked ATPase tiers D1 catalytic and D2 structural. Adaptor alpha-SNAP soluble attachment protein binds grooves along rod-like bundle via tetratricopeptide repeats and recruits NSF via N domains interaction with SNAP C-terminus. ATP hydrolysis in D1 causes power stroke threading SNARE polypeptide through central pore with tyr

Ref: Lodish et al., MCB Chapter 14: NSF and alpha-SNAP disassemble cis-SNARE complexes via ATP hydrolysis.

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Cell Signaling ELR Pathways - I

Activation of which small GTPase helps vesicle fusion in GLUT4 transport?

RALA, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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