Friction-driven membrane scission by the human ESCRT-III proteins CHMP1B and IST1

Abstract

The endosomal sorting complexes required for transport (ESCRT) system is an ancient and ubiquitous membrane scission machinery that catalyzes the budding and scission of membranes. ESCRT-mediated scission events, exemplified by those involved in the budding of HIV-1, are usually directed away from the cytosol (“reverse topology”), but they can also be directed toward the cytosol (“normal topology”). The ESCRT-III subunits CHMP1B and IST1 can coat and constrict positively curved membrane tubes, suggesting that these subunits could catalyze normal topology membrane severing. CHMP1B and IST1 bind and recruit the microtubule-severing AAA + ATPase spastin, a close relative of VPS4, suggesting that spastin could have a VPS4-like role in normal-topology membrane scission. Here, we reconstituted the process in vitro using membrane nanotubes pulled from giant unilamellar vesicles using an optical trap in order to determine whether CHMP1B and IST1 are capable of membrane severing on their own or in concert with VPS4 or spastin. CHMP1B and IST1 copolymerize on membrane nanotubes, forming stable scaffolds that constrict the tubes, but do not, on their own, lead to scission. However, CHMP1B–IST1 scaffolded tubes were severed when an additional extensional force was applied, consistent with a friction-driven scission mechanism. We found that spastin colocalized with CHMP1B-enriched sites but did not disassemble the CHMP1B–IST1 coat from the membrane. VPS4 resolubilized CHMP1B and IST1 without leading to scission. These observations show that the CHMP1B–IST1 ESCRT-III combination is capable of severing membranes by a friction-driven mechanism that is independent of VPS4 and spastin.

Dynamin A as a one-component division machinery for synthetic cells

“…The dots indicate the position of the proteins with respect to the membrane and colours correspond to the protein names listed. The membrane remodelling activity of all these proteins has been confirmed by previous in vitro reconstitutions 15,29,34–37 , while the scission activity of bacterial DynA is established here. (b) Schematics representing membrane fusion via a hemi-fusion intermediate with DynA (in green) reconstituted on the outer leaflet.…”

The patterned assembly and stepwise Vps4-mediated disassembly of composite ESCRT-III polymers drives archaeal cell division

“…Although the precise mechanism by which ESCRT-III proteins and Vps4 remodel and cut membranes remains an unresolved question in the field, purified ESCRT-III proteins have been shown to form composite polymers that assume a wide variety of forms, from flat spirals, to cones and helices (7)(8)(9)(10)(11)(12). In addition, reconstitution experiments have shown that ESCRT-III copolymers can undergo stepwise changes in their composition in the presence of ATP and Vps4, which can drive changes in membrane curvature that lead to membrane tube formation and, ultimately, membrane scission (13)(14)(15)(16)(17). Furthermore, physical computational models of the process show that sequential changes in polymer structure are likely sufficient to drive membrane remodelling and scission (18,19).…”

Mechanochemical rules for shape-shifting filaments that remodel membranes

“…To reproduce the unbinding sequence observed in experiment, we find that our filament rigidity needs to be between 3 and 7-fold larger than previous estimates [13, 25]. This apparent mismatch is due to the fact is that our passive model does not account for active energy supply, while in experiments dynamic disassembly is only observed upon addition of ATPase Vps4, which unfolds monomers and extracts them from the filament [9, 10, 27–31]. This led us to explore whether a Vps4-like activity that promotes stress-dependent polymer disassembly could aid the process.…”