ATP-dependent force generation and membrane scission by ESCRT-III and Vps4

Abstract

The ESCRTs catalyze reverse-topology scission from the inner face of membrane necks in HIV budding, multivesicular endosome biogenesis, cytokinesis, and other pathways. We encapsulated ESCRT-III subunits Snf7, Vps24, and Vps2, and the AAA+ ATPase Vps4 such that membrane nanotubes reflecting the correct topology of scission could be pulled from giant vesicles. Upon ATP release by photo-uncaging, this system was capable of generating forces within the nanotubes in a manner dependent upon Vps4 catalytic activity and Vps4 coupling to the ESCRT-III proteins. Imaging of scission revealed Snf7 and Vps4 puncta within nanotubes whose presence followed ATP release, correlated with force generation and nanotube constriction, and preceded scission. These observations directly verify long-standing predictions that ATP-hydrolyzing assemblies of ESCRT-III and Vps4 sever membranes.

Structures, Functions, and Dynamics of ESCRT-III/Vps4 Membrane Remodeling and Fission Complexes

“…In this model, extruded membranes would be drawn together and a cargo-filled vesicle released from the end of the tubule when the ESCRT-III filaments pulled on the tubule base by retracting back out of the tubule to readopt a planar configuration. This idea is supported by the recent demonstration that ESCRT-III/Vps4 complexes can assemble within the necks of synthetic membrane tubules and convert the energy of ATP hydrolysis into axial pulling forces that can sever the tubules (Schoeneberg et al 2018). As in coning models, changes in the magnitude and direction of filament tension could be dictated by altering subunit compositions during polymerization or by Vps4-dependent changes such as filament bundling, subunit exchange, depolymerization, or severing.…”

“…A series of models have been proposed to explain how ESCRT-III filaments and Vps4 together catalyze membrane remodeling, constriction, and fission (Adell et al 2017, Chiaruttini & Roux 2017, Fabrikant et al 2009, Hanson et al 2008, Henne et al 2013, Johnson et al 2018, Lenz et al 2009, Peel et al 2011, Saksena et al 2009, Schoeneberg et al 2018, Schöneberg et al 2017) (Figure 6). A consensus model has not emerged, however, and different aspects of the divergent models may need to be combined to explain how the ESCRT machinery can remodel membranes across such a variety of spatial scales and membrane geometries.…”

“…In an alternative class of models, membrane extrusion and fission are driven by filament buckling and unbuckling (Chiaruttini & Roux 2017, Chiaruttini et al 2015, Lenz et al 2009, Schoeneberg et al 2018). As illustrated in Figure 6 d , this elegant model envisions that ESCRT-III filaments initially spiral on a flat planar membrane, as is seen in the EM images in Figure 1 b , c .…”

Distinct domain requirements for EAP45 in HIV budding, late endosomal recruitment, and cytokinesis

“…The core of the ESCRT machinery comprises ESCRT-I (TSG101, VPS28, VPS37, and MVB12/UBAP1), -II (EAP20, EAP30, and EAP45) and -III (CHMP1-7) acting in a sequentially coordinated manner during membrane scission (1). The ESCRT machinery also has two other associated complexes, ESCRT-0 which precedes early cargo recruitment, and VPS4 AAA ATPase which universally acts at a late stage for membrane scission (2).…”

Actin modulates shape and mechanics of tubular membranes

“…For example, flat membrane surfaces within the endoplasmic reticulum mature into highly curved cylinders and spheres (1). In particular, trafficking involves tubular intermediates pulled by 5 molecular motors walking on microtubules (2). These dynamical rearrangements of membranes motivated the identification and the study of specialized proteins that bind to the membrane and directly act on its curvature (3-5).…”