Practice question

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.