Multivalent Rab interactions determine tether-mediated membrane fusion

Lürick, Anna; Gao, Jieqiong; Kuhlee, Anne; Yavavli, Erdal; Langemeyer, Lars; Perz, Angela; Raunser, Stefan; Ungermann, Christian

doi:10.1091/mbc.e16-11-0764

Cited by 57 publications

(81 citation statements)

References 52 publications

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“…Since this is not observed, the Vps8 subunit is likely primarily responsible for the differential steady-state location of most CORVET complexes. This idea is broadly consistent with experiments in yeast HOPS, showing that the Rab-binding subunits Vsp39 and Vps41 have different binding properties (Lurick et al, 2017). Vsp39 and Vps41 are positioned at opposite ends of the extended barbell-like cryoEM structure of yeast HOPS, consistent with independent binding and with the idea that relative Rab affinities could determine steady state localization (Brocker et al, 2012).…”

Section: Discussionsupporting

confidence: 85%

Diversification of CORVET tethers facilitates transport complexity inTetrahymena thermophila

Sparvoli

Zoltner

Field

et al. 2019

Preprint

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In endolysosomal networks, two hetero-hexameric tethers called HOPS and CORVET are found widely throughout eukaryotes. The unicellular ciliate Tetrahymena thermophila possesses elaborate endolysosomal structures, but curiously both it and related protozoa lack the HOPS tether and several other trafficking genes while retaining the related CORVET complex. Tetrahymena encodes multiple paralogs of most CORVET subunits, which assemble into six distinct complexes. Each complex has a unique subunit composition and, significantly, shows unique localization, indicating participation in distinct pathways. One pair of complexes differ by a single subunit (Vps8), but have late endosomal vs. recycling endosome locations. While Vps8 subunits are thus prime determinants for targeting and functional specificity, determinants exist on all subunits except Vps11. This unprecedented expansion and diversification of CORVET provides a potent example of tether flexibility, and illustrates how 'backfilling' following secondary losses of trafficking genes can provide a mechanism for evolution of new pathways. 3

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Section: Discussionsupporting

confidence: 85%

Diversification of CORVET tethers facilitates transport complexity inTetrahymena thermophila

Sparvoli

Zoltner

Field

et al. 2019

Preprint

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“…A closing pore actively pushes the SNAREs out of its interior (Fig B). This movement should be hindered by the stiffness and the length of the SNARE complex, as well as by its attachment to HOPS, which is anchored in both membranes (Ho & Stroupe, ; Lürick et al , ). It is therefore plausible that a pore lined by multiple SNARE complexes displays a larger stability against hemifission, in line with experimental observations (Shi et al , ; Bao et al , ).…”

Section: Resultsmentioning

confidence: 99%

“…Homotypic fusion of yeast vacuoles in vitro could be dissected into a series of well‐characterized steps: Priming by Sec18/NSF promotes SNARE activation through dissociation of cis‐SNARE complexes (Mayer et al , ; Ungermann et al , ). Tethering, governed by coordinated action of the Rab‐GTPase Ypt7 and the HOPS complex, permits the formation of trans‐SNARE complexes (Mayer & Wickner, ; Price et al , ; Zick & Wickner, ; Orr et al , ; Lürick et al , ). These, together with V 0 proteolipids, induce lipid mixing (Peters et al , ; Reese et al , ; Strasser et al , ; Desfougères et al , ; Mattie et al , ).…”

Section: Introductionmentioning

confidence: 99%

SNARE ‐mediated membrane fusion arrests at pore expansion to regulate the volume of an organelle

et al. 2018

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Constitutive membrane fusion within eukaryotic cells is thought to be controlled at its initial steps, membrane tethering and SNARE complex assembly, and to rapidly proceed from there to full fusion. Although theory predicts that fusion pore expansion faces a major energy barrier and might hence be a rate-limiting and regulated step, corresponding states with non-expanding pores are difficult to assay and have remained elusive. Here, we show that vacuoles in living yeast are connected by a metastable, non-expanding, nanoscopic fusion pore. This is their default state, from which full fusion is regulated. Molecular dynamics simulations suggest that SNAREs and the SM protein-containing HOPS complex stabilize this pore against re-closure. Expansion of the nanoscopic pore to full fusion can thus be triggered by osmotic pressure gradients, providing a simple mechanism to rapidly adapt organelle volume to increases in its content. Metastable, nanoscopic fusion pores are then not only a transient intermediate but can be a long-lived, physiologically relevant and regulated state of SNARE-dependent membrane fusion.

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“…These subunits are replaced in HOPS by Vps39 and Vps41, switching the binding specificity to Rab7‐like GTPase Ypt7 in yeast . Two binding sites for the same GTPase are the key feature of CORVET and HOPS that allows these complexes to engage and tether homotypic membranes . In metazoan HOPS, this specificity seems to have shifted to other small GTPases.…”

Section: Class C Vps Tethersmentioning

confidence: 99%

Structure of membrane tethers and their role in fusion

Ungermann

Kümmel

2019

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Vesicular transport between different membrane compartments is a key process in cell biology required for the exchange of material and information. The complex machinery that executes the formation and delivery of transport vesicles has been intensively studied and yielded a comprehensive view of the molecular principles that underlie the budding and fusion process. Tethering also represents an essential step in each trafficking pathway. It is mediated by Rab GTPases in concert with so-called tethering factors, which constitute a structurally diverse family of proteins that share a similar role in promoting vesicular transport. By simultaneously binding to proteins and/or lipids on incoming vesicles and the target compartment, tethers are thought to bridge donor and acceptor membrane. They thus provide specificity while also promoting fusion. However, how tethering works at a mechanistic level is still elusive.We here discuss the recent advances in the structural and biochemical characterization of tethering complexes that provide novel insight on how these factors might contribute the efficiency of fusion. K E Y W O R D S CATCHR, golgin, membrane fusion, Rab GTPases, Sec1/Munc18, SNARE, tethering, vesicular transport 1 | INTRODUCTION Compartmentalization of eukaryotic cells into organelles is the prerequisite for the formation of chemically distinct environments that allow the implementation of specialized functions. Communication and the exchange of substances between different membrane compartments, however, is also essential for proper function of cells. In the endomembrane system, comprising the secretory pathway and the endolysosomal system, membrane vesicles have long been established as transport carriers that fulfill this function. 1 Trafficking can be dissected into distinct steps: at the donor membrane, small GTPases like Arf, Sar1 or Arf-like (Arl) and coat proteins, which assemble into vesicle coat complexes, orchestrate cargo sorting and concentration followed by vesicle budding and scission. Vesicles are then transported along cytoskeletal filaments with the help of motor proteins. At the target membrane, incoming vesicles are recruited by Rab GTPases and tethering factors. Rabs are markers of organelle identity and conserved part of the fusion machinery. 2,3 Common to all small GTPases, Rabs cycle between an inactive GDP-bound and an active GTP-bound form, and only the latter form can interact with effectors that mediate downstream functions of Rabs. Tethering factors from different classes are evolutionarily unrelated proteins and structurally divers, but share a function as Rab effectors and are thought to bridge two opposing membranes. After tethering, SNAREs (soluble N-ethylmaleimide sensitive factor attachment protein receptor) on each membrane are necessary. 4 SNARE proteins drive fusion, but function of SNAREs requires S/M (Sec1/Munc18) family proteins that act as chaperones of SNARE assembly and the NSF (N-ethylmaleimide sensitive factor) ATPase that with the adaptor protein α-SNAP disasse...

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Multivalent Rab interactions determine tether-mediated membrane fusion

Abstract: The HOPS tethering complex binds both the Rab7-like Ypt7 and SNAREs. Several HOPS mutants are used to show that both Rab-binding sites, but not the ALPS motif in Vps41, are necessary to tether and fuse membranes.

Cited by 57 publications

References 52 publications

Diversification of CORVET tethers facilitates transport complexity inTetrahymena thermophila

Diversification of CORVET tethers facilitates transport complexity inTetrahymena thermophila

SNARE ‐mediated membrane fusion arrests at pore expansion to regulate the volume of an organelle

Structure of membrane tethers and their role in fusion

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