Membrane Constriction and Thinning by Sequential ESCRT-III Polymerization

Abstract

The Endosomal Sorting Complexes Required for Transport (ESCRTs) mediate diverse membrane remodeling events. These typically require ESCRT-III proteins to stabilize negatively-curved membranes, although recent work has indicated that certain ESCRT-IIIs also participate in positive-curvature membrane shaping reactions. ESCRT-IIIs polymerize into membrane-binding filaments, but the structural basis for negative versus positive membrane remodeling by these proteins remains poorly understood. To learn how certain ESCRT-IIIs shape positively-curved membranes, we determined structures of human membrane-bound CHMP1B-only, membranebound CHMP1B+IST1, and IST1-only filaments by electron cryomicroscopy. Our structures show how CHMP1B first polymerizes into a single-stranded helical filament, shaping membranes into moderate-curvature tubules. Subsequently, IST1 assembles a second strand upon CHMP1B, further constricting the membrane tube and reducing its diameter nearly to the fission point. Each Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Principles of membrane remodeling by dynamic ESCRT-III polymers

“…while maintaining the hairpin of the closed state, hence disrupting the interaction between helix α4 and the hairpin and leading to a more elongated form, as shown for full-length human CHMP1B [9,10] and truncated forms of CHMP4/Shrub/Snf7 from Drosophila melanogaster [11] and S. cerevisiae [12] (Figure 1A). Yeast Vps24 displays an intermediate, semi-open conformation without the packing of α3 and α4 to the hairpin of the closed conformation, but also without the α2-3 merger and full elongation of the open conformation [13] (Figure 1A).…”

“…These proteins all share a core structure that is proposed to adopt different conformations. In their closed state, they form a four-helix bundle; the longer helices, α1 and α2, form a hairpin, with the shorter helices, α3 and α4, packed against the hairpin, as shown for CHMP3 [7,8] and IST1 [9,10] (Figure 1A). In their open state, helices α2 and α3 merge into a single helix α2-3…”

NPC1-mTORC1 Signaling Couples Cholesterol Sensing to Organelle Homeostasis and Is a Targetable Pathway in Niemann-Pick Type C

“…Recently, it has emerged that the lysosomal limiting membrane is susceptible to damage resulting from undigested/undigestible substrates that accumulate within the lumen (Jia et al, 2020;Maejima et al, 2013;Radulovic et al, 2018;Skowyra et al, 2018). An early detection system provided by the endosomal sorting complex required for transport (ESCRT) III proteins detects ''microtears'' in the lysosomal membrane and repairs them via a scission process thought to topologically resemble intraluminal vesicle budding during endosomal maturation (Nguyen et al, 2020;Radulovic et al, 2018;Schö neberg et al, 2017;Skowyra et al, 2018). Suggestive of ongoing damage to NPC lysosome membranes, our proteomics analysis of NPC lysosomes found a significant enrichment of the ESCRT III components CHMP1A and IST1, along with ALIX/ PDCD6IP, which provides a recruiting platform for the assembly of coiled ESCRT III filaments (Radulovic et al, 2018;Skowyra et al, 2018) (Figure 2A and Table S1).…”

PspA adopts an ESCRT-III-like fold and remodels bacterial membranes

“…More recently, polymers assembled from full-length ESCRT-III were elucidated at near-atomic resolution using cryo-EM: human IST1 and CHMP1B form a hetero-polymer with a compact and extended conformation forming a tubular assembly (McCullough et al, 2015), whereas yeast Vps24 assembles in a double-stranded filament composed of domain-swapped dimers in the extended conformation (Huber et al, 2020). The structures of IST1/CHMP1B tubes confirmed the presence of a lipid bilayer in the lumen of the assemblies (Nguyen et al, 2020). Thus, IST1/CHMP1B is capable of constricting vesicles and inducing positive membrane curvature suitable for opposite ESCRT topology membrane processes.…”