Figure 3.

ESCRT-III. a. Assembled ESCRT-III polymer is visualized in this electron micrograph showing the filaments underlying buds and tubules emerging from the top of a cell overexpressing human SNF7 and an inactive mutant of VPS4B. Image is reproduced, with permission, from²¹. The SNF7-containing filaments are seen because of post-fixation extraction with detergent. b. Helical organization of individual ESCRT-III proteins based on the observed structure of human VPS24³³,⁵⁸. Helices α1– α4 form the core of the protein responsible for membrane binding and polymer assembly and are regulated by autoinhibitory sequences in α5 and the C-terminal MIM1 (not resolved in the CHMP3 structure). All ESCRT-III proteins contain the α1– α4 core and the α5 autoinhibitory sequence. Vps2, Did2, and Vps24 contain a C-terminal MIM1 motif, whereas Vps20 and Snf7 contain a C-terminal MIM2 motif. Ist1 has both MIM1 and MIM2 motifs at its C-terminus. Both types of MIM bind to the MIT domain of Vps4, but they do so at separate sites and do not compete with one another. c. Cycle of ESCRT-III assembly and VPS4-mediated disassembly. ESCRT-III proteins are in a `closed' and monomeric conformation in the cytosol, with intramolecular autoinhibitory interactions preventing membrane binding and polymer assembly. In their `open' conformation, these autoinhibitory interactions are released, and the subunits bind to each other and to the membrane as they assemble into functional ESCRT-III polymers.

-This could be redrawn with colors that fit better w/ rest of figs