Skip to content
Login Register

#vesicle scission

3 public questions tagged with this topic.

Protein Sorting and Trafficking

Which protein is required for vesicle scission during receptor-mediated endocytosis?

Final separation stage clathrin-coated pit formation yielding free vesicle requires enzymatic fission beyond coat polymerization. Clathrin assembly with adaptor AP2 and BAR proteins epsin, amphiphysin, endophilin generates deeply invaginated bud connected plasma membrane narrow tubule neck diameter around 20 nm bilayer. Separation demands mechanical constriction cutting neck. Specialist protein dynamin large 96 kDa GTPase family founding member N-terminal GTPase domain, middle stalk, PH domain binding PI(4,5)P2 enriched site, GED and PRD binding SH3, polymerizes helical collar around neck. Recruitment mediated curvature-sensing BAR proteins generating curvature. Stoichiometry about 13 dimers per turn aligns G domains efficient hydrolysis. GTP binding tightens helix reducing lumen radius; cooperative hydrolysis drives constriction twisting shear breaking membrane hemi-fission intermediate releasing vesicle. Clathrin provides structural cage not enzymatic fission; Rab GTPases regulate downstream tethering early endosome via EEA1, SNAREs mediate subsequent fusion after uncoating. Temperature-sensitive shibire mutant drosophila dynamin blocks synaptic vesicle recycling restrictive temperature trapping pits long collars demonstrating indispensable scission function receptor-mediated endocytosis essential cellular uptake.

Ref: Kaksonen & Roux, Nat Rev Mol Cell Biol: Dynamin scission in clathrin-mediated endocytosis.

View Details
Protein Sorting and Trafficking

The process of vesicle scission during clathrin-mediated endocytosis requires:

Formation of endocytic vesicle demands energetically unfavorable fission of neck connecting bud to parent membrane against line tension and bending resistance. In clathrin-mediated pathway adaptor AP2 and accessory proteins FCHo, epsin together with clathrin lattice driving polymerization stabilize deeply invaginated bud with omega shape. Constriction of neck performed by dynamin large 96 kDa GTPase assembling into helical oligomer about two turns around neck 50 nm diameter PH domain binding PI(4,5)P2. Polymerization aligns G domains enhancing GTPase 100 fold. Upon concerted GTP binding and cooperative hydrolysis helix compacts from 20 nm to 4 nm radius and twist extends producing high curvature shear stress breaking membrane continuum executing hemi-fission then full fission releasing coated vesicle. Actin polymerization via Arp2/3 and cortactin assists under high tension at apical membranes. SNARE interactions drive downstream fusion with early endosome after uncoating, NSF ATPase disassembles cis-SNAREs post-fusion, Rab5 GTP hydrolysis coordinates early tethering but not scission. Dominant negative dynamin K44A unable to bind GTP arrests pits as elongated tubules. Therefore vesicle scission uniquely depends dynamin-mediated GTP hydrolysis providing mechanoenzyme activity essential for endocytosis.

Ref: Schmid & Frolov, Annu Rev Cell Dev Biol: Dynamin GTP hydrolysis drives membrane scission.

View Details
Protein Sorting and Trafficking

What is the role of dynamin in clathrin-coated vesicle formation?

Clathrin-coated vesicle formation ends with detachment step demanding membrane remodeling fission against line tension. While clathrin lattice with adaptor AP2 and accessory proteins like epsin concentrate cargo and deform membrane into omega pit, polymerization does not cut bilayer. Instead large GTPase dynamin recruited via SH3 interactions with amphiphysin, endophilin, intersectin binding proline-rich domain. Dynamin 100 kDa possesses G domain, PH domain binding PI(4,5)P2, stalk for dimerization and GED. It assembles into helical polymer around vesicle neck about 13 dimers per turn. Upon GTP binding and cooperative hydrolysis helix undergoes constriction reducing lumen from 20 nm to below 2 nm and twistase motion generating torsional strain causing hemi-fission then full fission releasing coated vesicle. Dynamin does not select cargo nor directly bind SNAREs, and does not degrade coats; coat removal separate Hsc70-auxilin ATPase reaction. In synapses dynamin1 knockout causes accumulation of coated intermediates with long necks. Small molecule dynasore blocking GTPase prevents scission demonstrating essential GTP-dependent fission activity.

Ref: Alberts et al., MBC Chapter 13: Dynamin GTPase mediates vesicle scission in endocytosis.

View Details