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#clathrin-coated vesicles

2 public questions tagged with this topic.

Protein Sorting and Trafficking

Which of the following does NOT require clathrin-coated vesicles?

Coat identity determines vesicle origin and destination providing directional logic to secretory pathway. COPII composed of Sar1 initiating curvature, inner adaptor Sec23-Sec24 binding cargo export signals, outer cage Sec13-Sec31 polymerizing into cuboctahedron operates exclusively at ER exit sites producing vesicles moving toward ERGIC and cis-Golgi carrying newly synthesized secretory proteins bearing ER exit motifs DXE, LXXLE. COPI composed of ARF1-GTP and heptameric coatomer operates reciprocally at Golgi rims and ERGIC retrieving material backward including KKXX membrane proteins and KDEL receptor bound luminal chaperones. Clathrin triskelia with heterotetrameric adaptors AP1 at TGN, AP2 at plasma membrane, GGAs and AP3 operates at later stations where PI4P or PI(4,5)P2 and ARF family GTPases recruit adaptors: TGN to late endosomes for mannose-6-phosphate receptor bound hydrolases, plasma membrane to early endosomes for transferrin uptake, and endosomes to lysosomes. Thus ER to Golgi uniquely COPII dependent mechanistically independent of clathrin lattice. siRNA of clathrin heavy chain blocks transferrin endocytosis and cathepsin D sorting but not ER export of temperature-sensitive VSV-G, while Sec24B depletion arrests ER exit confirming distinct machinery division and functional separation.

Ref: Alberts et al., MBC: COPII ER-to-Golgi transport does not require clathrin coats.

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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.

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