Structural Analysis of the Ribosome-associated Complex (RAC) Reveals an Unusual Hsp70/Hsp40 Interaction

Fiaux, Jocelyne; Horst, Janina; Scior, Annika; Preißler, Steffen; Koplin, Ansgar; Bukau, Bernd; Deuerling, Elke

doi:10.1074/jbc.m109.075804

Cited by 27 publications

(17 citation statements)

References 23 publications

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“…Given the high abundance of Ssa1/2 in prion aggregates relative to other factors required for fiber severing, e.g., Hsp104 (34), it may serve an additional function. A recent study of a ribosome-associated Hsp70-40 complex, Ssz-zuotin, suggests an end-to-end binding of these two components, which could generate an extended assembly (57). By analogy, elongated structures could be formed by Ssa1/2 and Sis1, and either serve a scaffolding function and/or regulate access of other factors, thereby influencing the processing of prion fibrils.…”

Section: Discussionmentioning

confidence: 99%

Heritable yeast prions have a highly organized three-dimensional architecture with interfiber structures

Saibil

Seybert

Habermann

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Yeast prions constitute a "protein-only" mechanism of inheritance that is widely deployed by wild yeast to create diverse phenotypes. One of the best-characterized prions, [PSI + ], is governed by a conformational change in the prion domain of Sup35, a translation-termination factor. When this domain switches from its normal soluble form to an insoluble amyloid, the ensuing change in protein synthesis creates new traits. Two factors make these traits heritable: (i) the amyloid conformation is self-templating; and (ii) the protein-remodeling factor heat-shock protein (Hsp)104 (acting together with Hsp70 chaperones) partitions the template to daughter cells with high fidelity. Prions formed by several other yeast proteins create their own phenotypes but share the same mechanistic basis of inheritance. Except for the amyloid fibril itself, the cellular architecture underlying these protein-based elements of inheritance is unknown. To study the 3D arrangement of prion assemblies in their cellular context, we examined yeast [PSI + ] prions in the native, hydrated state in situ, taking advantage of recently developed methods for cryosectioning of vitrified cells. Cryo-electron tomography of the vitrified sections revealed the prion assemblies as aligned bundles of regularly spaced fibrils in the cytoplasm with no bounding structures. Although the fibers were widely spaced, other cellular complexes, such as ribosomes, were excluded from the fibril arrays. Subtomogram image averaging, made possible by the organized nature of the assemblies, uncovered the presence of an additional array of densities between the fibers. We suggest these structures constitute a self-organizing mechanism that coordinates fiber deposition and the regulation of prion inheritance.

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Section: Discussionmentioning

confidence: 99%

Heritable yeast prions have a highly organized three-dimensional architecture with interfiber structures

Saibil

Seybert

Habermann

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…Zuo1 forms a stable heterodimer (often called the ribosome associated complex, RAC) with an atypical Hsp70 (called Ssz1 and HspA14 in fungi and humans, respectively), tethering it to the ribosome 15–18 . Ssz1/HspA14 bind, but do not hydrolyze, ATP and thus cannot partner with a J protein and perform the classic client protein binding cycle 12,19,20 .…”

Section: Introductionmentioning

confidence: 99%

Dual interaction of the Hsp70 J-protein cochaperone Zuotin with the 40S and 60S ribosomal subunits

Lee

Sharma

Shrestha

et al. 2016

Nat Struct Mol Biol

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Ribosome-associated J protein-Hsp70 chaperones promote nascent polypeptide folding and normal translational fidelity. Though known to span the ribosome subunits, understanding of J protein Zuo1 function is limited. New structural and crosslinking data allow more precise positioning of Saccharomyces cerevisiae Zuo1 near the 60S polypeptide exit site, pointing to interactions with ribosomal protein eL31 and 25S rRNA helix 24. The junction between the 60S-interacting and subunit-spanning helices is a hinge, positioning Zuo1 on the 40S, yet accommodating subunit rotation. Interaction between C-terminus of Zuo1 and 40S occurs via 18S rRNA expansion segment 12 (ES12) of helix 44, which originates at the decoding site. Deletions in either ES12 or C-terminus of Zuo1 alter stop codon readthrough and −1 frameshifting. Our study offers insight into how this cotranslational chaperone system may monitor decoding site activity and nascent polypeptide transit, thereby coordinating protein translation and folding.

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“…Given that Hsc70 and Hsp110 may form stable 1:1 heterodimers (Polier et al 2008) capable of disaggregating stable protein aggregates (Rampelt et al 2012;Shorter 2011), the observed stoichiometry in the cytosol suggests that all three types of Hsp110s can form functional disaggregating complexes with 24 % the Hsp70 pool, leaving the remaining 76 % to carry other Hsc70-specific functions, such as deoligomerization of clathrin cages (Sousa and Lafer 2006), inactivating native oligomers (Weiss et al 2007), and mediating the folding of nascent polypeptides . Upon being anchored to the L31 ribosomal subunit near the ribosome exit, the J-domain cochaperone zuotin (DNAJC2) can recruit cytosolic HspA14 (Hsp70L1) and Hsc70 to assist the folding of nascent polypeptides (Fiaux et al 2010). Examining the cellular amounts showed that whereas zuotin and HspA14 were equimolar, they both were about 45-fold less abundant than the L31 ribosomal anchor (Table 1).…”

Section: The Hsp70 Chaperone Systems In Hela Cellsmentioning

confidence: 99%

Proteomic data from human cell cultures refine mechanisms of chaperone-mediated protein homeostasis

Finka

Goloubinoff

2013

Cell Stress and Chaperones

184

209

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In the crowded environment of human cells, folding of nascent polypeptides and refolding of stressunfolded proteins is error prone. Accumulation of cytotoxic misfolded and aggregated species may cause cell death, tissue loss, degenerative conformational diseases, and aging. Nevertheless, young cells effectively express a network of molecular chaperones and folding enzymes, termed here "the chaperome," which can prevent formation of potentially harmful misfolded protein conformers and use the energy of adenosine triphosphate (ATP) to rehabilitate already formed toxic aggregates into native functional proteins. In an attempt to extend knowledge of chaperome mechanisms in cellular proteostasis, we performed a meta-analysis of human chaperome using high-throughput proteomic data from 11 immortalized human cell lines. Chaperome polypeptides were about 10 % of total protein mass of human cells, half of which were Hsp90s and Hsp70s. Knowledge of cellular concentrations and ratios among chaperome polypeptides provided a novel basis to understand mechanisms by which the Hsp60, Hsp70, Hsp90, and small heat shock proteins (HSPs), in collaboration with cochaperones and folding enzymes, assist de novo protein folding, import polypeptides into organelles, unfold stress-destabilized toxic conformers, and control the conformal activity of native proteins in the crowded environment of the cell. Proteomic data also provided means to distinguish between stable components of chaperone core machineries and dynamic regulatory cochaperones.

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Structural Analysis of the Ribosome-associated Complex (RAC) Reveals an Unusual Hsp70/Hsp40 Interaction

Cited by 27 publications

References 23 publications

Heritable yeast prions have a highly organized three-dimensional architecture with interfiber structures

Heritable yeast prions have a highly organized three-dimensional architecture with interfiber structures

Dual interaction of the Hsp70 J-protein cochaperone Zuotin with the 40S and 60S ribosomal subunits

Proteomic data from human cell cultures refine mechanisms of chaperone-mediated protein homeostasis

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