A dual role of the ribosome-bound chaperones RAC/Ssb in maintaining the fidelity of translation termination

Abstract The yeast ribosome-associated complex RAC and the Hsp70 homolog Ssb are anchored to the ribosome and together act as chaperones for the folding and co-translational assembly of nascent polypeptides. In addition, the RAC/Ssb system plays a crucial role in maintaining the fidelity of translation termination; however, the latter function is poorly understood. Here we show that the RAC/Ssb system promotes the fidelity of translation termination via two distinct mechanisms. First, via direct contacts with the ribosome and the nascent chain, RAC/Ssb facilitates the translation of stalling-prone poly-AAG/A sequences encoding for polylysine segments. Impairment of this function leads to enhanced ribosome stalling and to premature nascent polypeptide release at AAG/A codons. Second, RAC/Ssb is required for the assembly of fully functional ribosomes. When RAC/Ssb is absent, ribosome biogenesis is hampered such that core ribosomal particles are structurally altered at the decoding and peptidyl transferase centers. As a result, ribosomes assembled in the absence of RAC/Ssb bind to the aminoglycoside paromomycin with high affinity (KD = 76.6 nM) and display impaired discrimination between stop codons and sense codons. The combined data shed light on the multiple mechanisms by which the RAC/Ssb system promotes unimpeded biogenesis of newly synthesized polypeptides.

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Structural basis of GTPase-mediated mitochondrial ribosome biogenesis and recycling

Nature Communications ◽

10.1038/s41467-021-23702-y ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Hauke S. Hillen ◽

Elena Lavdovskaia ◽

Franziska Nadler ◽

Elisa Hanitsch ◽

Andreas Linden ◽

...

Keyword(s):

Ribosomal Proteins ◽

Ribosome Biogenesis ◽

Ribosomal Subunit ◽

Structural Basis ◽

Peptidyl Transferase ◽

Mitochondrial Ribosomes ◽

Mitochondrial Ribosome ◽

In Vitro Reconstitution

AbstractRibosome biogenesis requires auxiliary factors to promote folding and assembly of ribosomal proteins and RNA. Particularly, maturation of the peptidyl transferase center (PTC) is mediated by conserved GTPases, but the molecular basis is poorly understood. Here, we define the mechanism of GTPase-driven maturation of the human mitochondrial large ribosomal subunit (mtLSU) using endogenous complex purification, in vitro reconstitution and cryo-EM. Structures of transient native mtLSU assembly intermediates that accumulate in GTPBP6-deficient cells reveal how the biogenesis factors GTPBP5, MTERF4 and NSUN4 facilitate PTC folding. Addition of recombinant GTPBP6 reconstitutes late mtLSU biogenesis in vitro and shows that GTPBP6 triggers a molecular switch and progression to a near-mature PTC state. Additionally, cryo-EM analysis of GTPBP6-treated mature mitochondrial ribosomes reveals the structural basis for the dual-role of GTPBP6 in ribosome biogenesis and recycling. Together, these results provide a framework for understanding step-wise PTC folding as a critical conserved quality control checkpoint.

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‘Volunteering is like any other business’: Civic participation and social media

New Media & Society ◽

10.1177/1461444817731920 ◽

2017 ◽

Vol 20 (6) ◽

pp. 2186-2207 ◽

Cited By ~ 11

Author(s):

Anne Kaun ◽

Julie Uldam

Keyword(s):

Social Media ◽

Crucial Role ◽

Power Relations ◽

Civic Participation ◽

Analytical Framework ◽

Migration Crisis ◽

Technological Affordances ◽

Shed Light

The increased influx of refugees in 2015 has led to challenges in transition and destination countries such as Germany, Sweden and Denmark. Volunteer-led initiatives providing urgent relief played a crucial role in meeting the needs of arriving refugees. The work of the volunteers in central stations and transition shelters was mainly organised with the help of Facebook, in terms of both inward and outward communications. This article examines the role of social media for civic participation drawing on Swedish volunteer initiatives that emerged in the context of the migration crisis in 2015 as a case study. Theoretically, this article provides an analytical framework, including power relations, technological affordances, practices and discourses, which helps shed light on the interrelation between social media and civic participation.

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Islamization, Gentrification and Domestication: ‘A Girls’ Islamic Course' and Rural Muslims in Western Uttar Pradesh

Modern Asian Studies ◽

10.1017/s0026749x040010015 ◽

2004 ◽

Vol 38 (1) ◽

pp. 1-53 ◽

Cited By ~ 22

Author(s):

Patricia Jeffery ◽

Roger Jeffery ◽

Craig Jeffrey

Keyword(s):

Nineteenth Century ◽

Twentieth Century ◽

Crucial Role ◽

Uttar Pradesh ◽

Religious Practice ◽

North India ◽

September 11Th ◽

Early Twentieth Century ◽

Shed Light

Girls' education has been enduringly controversial in north India, and the disputes of the second half of the nineteenth century and early twentieth century still echo in debates about girls' education in contemporary India. In this paper, we reflect on the education of rural Muslim girls in contemporary western Uttar Pradesh (UP), by examining an Islamic course for girls [Larkiyon kā Islālmī Course], written in Urdu and widely used in madrasahs there. First, we summarize the central themes in the Course: purifying religious practice; distancing demure, self-controlled, respectable woman from the lower orders; and the crucial role of women as competent homemakers. Having noted the conspicuous similarities between these themes and those in the nineteenth and early twentieth-century textbooks and advice manuals for girls and women, the second section examines the context in which the earlier genre emerged. Finally, we return to the present day. Particularly since September 11th 2001, madrasahs have found themselves the focus of hostile allegations that bear little or no relationship to the activities of the madrasahs that we studied. Nevertheless, madrasah education does have problematic implications. The special curricula for girls exemplifies how a particular kind of élite project has been sustained and transformed, and we aim to shed light on contemporary communal and class issues as well as on gender politics.

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Testing the Semantic Homogeneity Constraint

Journal of Historical Linguistics ◽

10.1075/jhl.4.2.01nes ◽

2014 ◽

Vol 4 (2) ◽

pp. 161-191 ◽

Cited By ~ 1

Author(s):

Tore Nesset ◽

Anastasia Makarova

Keyword(s):

Empirical Evidence ◽

Present Article ◽

Crucial Role ◽

Language Change ◽

Historical Linguistics ◽

Semantic Factor ◽

Homogeneous Domains ◽

General Linguistics ◽

Shed Light

Although it has been widely assumed in historical linguistics that semantics plays a crucial role in analogical change, it is difficult to pinpoint the contribution of the semantic factor, since meaning and form work closely together in bringing about language change. The purpose of the present article is to shed light on the issue by means of two case studies from Russian, which enable us to isolate the role of semantics. The hypothesis we test is that analogical change is restricted to semantically homogeneous domains. We call this the Semantic Homogeneity Constraint. Two phenomena from Russian conjugation are explored: suffix shift and NU-drop. Although they seem parallel, analogical change occurs in the former, but not in the latter. It is argued that this is because the verbs involved in suffix shift constitute a semantically homogeneous domain, within which analogical change can take place. By contrast, NU-verbs are semantically diverse, and these semantic differences create boundaries which block analogical change. The findings have implications both for Russian and general linguistics. While suffix shift and NU-drop are well-known phenomena in Russian conjugation, they have not been juxtaposed and compared before. Our comparison provides new insights about the differences and similarities of the two phenomena. From the perspective of historical linguistics, the present article contributes to the theory of analogy, insofar as we provide empirical evidence for the Semantic Homogeneity Constraint, which places restrictions on semantic domains where analogical change can take place.

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Role of the Cytoplasmic Segments of Sec61α in the Ribosome-Binding and Translocation-Promoting Activities of the Sec61 Complex

The Journal of Cell Biology ◽

10.1083/jcb.150.1.53 ◽

2000 ◽

Vol 150 (1) ◽

pp. 53-64 ◽

Cited By ~ 52

Author(s):

David Raden ◽

Weiqun Song ◽

Reid Gilmore

Keyword(s):

Protein Translocation ◽

Immunoblot Analysis ◽

Binding Activity ◽

Dual Function ◽

Cleavage Sites ◽

Critical Determinant ◽

Ribosome Binding ◽

High Affinity ◽

Nascent Chain

The Sec61 complex performs a dual function in protein translocation across the RER, serving as both the high affinity ribosome receptor and the translocation channel. To define regions of the Sec61 complex that are involved in ribosome binding and translocation promotion, ribosome-stripped microsomes were subjected to limited digestions using proteases with different cleavage specificities. Protein immunoblot analysis using antibodies specific for the NH2 and COOH terminus of Sec61α was used to map the location of proteolysis cleavage sites. We observed a striking correlation between the loss of binding activity for nontranslating ribosomes and the digestion of the COOH- terminal tail or cytoplasmic loop 8 of Sec61α. The proteolyzed microsomes were assayed for SRP-independent translocation activity to determine whether high affinity binding of the ribosome to the Sec61 complex is a prerequisite for nascent chain transport. Microsomes that do not bind nontranslating ribosomes at physiological ionic strength remain active in SRP-independent translocation, indicating that the ribosome binding and translocation promotion activities of the Sec61 complex do not strictly correlate. Translocation-promoting activity was most severely inhibited by cleavage of cytosolic loop 6, indicating that this segment is a critical determinant for this function of the Sec61 complex.

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Structural basis for selective stalling of human ribosome nascent chain complexes by a drug-like molecule

10.1101/315325 ◽

2018 ◽

Cited By ~ 3

Author(s):

Wenfei Li ◽

Fred R. Ward ◽

Kim F. McClure ◽

Stacey Tsai-Lan Chang ◽

Elizabeth Montabana ◽

...

Keyword(s):

Small Molecules ◽

Translation Termination ◽

Structural Basis ◽

Small Subset ◽

Peptidyl Transferase ◽

Peptidyl Transferase Center ◽

Chain Complexes ◽

Nascent Chain ◽

Exit Tunnel ◽

Ribosome Exit Tunnel

AbstractSmall molecules that target the ribosome generally have a global impact on protein synthesis. However, the drug-like molecule PF-06446846 (PF846) binds the human ribosome and selectively blocks the translation of a small subset of proteins by an unknown mechanism. In high-resolution cryo-electron microscopy (cryo-EM) structures of human ribosome nascent chain complexes stalled by PF846, PF846 binds in the ribosome exit tunnel in a newly-identified and eukaryotic-specific pocket formed by the 28S ribosomal RNA (rRNA), and redirects the path of the nascent polypeptide chain. PF846 arrests the translating ribosome in the rotated state that precedes mRNA and tRNA translocation, with peptidyl-tRNA occupying a mixture of A/A and hybrid A/P sites, in which the tRNA 3’-CCA end is improperly docked in the peptidyl transferase center. Using mRNA libraries, selections of PF846-dependent translation elongation stalling sequences reveal sequence preferences near the peptidyl transferase center, and uncover a newly-identified mechanism by which PF846 selectively blocks translation termination. These results illuminate how a small molecule selectively stalls the translation of the human ribosome, and provides a structural foundation for developing small molecules that inhibit the production of proteins of therapeutic interest.

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Crucial Role of Bysl in Mammalian Preimplantation Development as an Integral Factor for 40S Ribosome Biogenesis

Molecular and Cellular Biology ◽

10.1128/mcb.01908-06 ◽

2007 ◽

Vol 27 (6) ◽

pp. 2202-2214 ◽

Cited By ~ 13

Author(s):

Kenjiro Adachi ◽

Chie Soeta-Saneyoshi ◽

Hiroshi Sagara ◽

Yoichiro Iwakura

Keyword(s):

Crucial Role ◽

Ribosome Biogenesis ◽

Molecular Mechanisms ◽

Cell Mass ◽

Embryonic Stem ◽

Ribosomal Subunit ◽

Preimplantation Development ◽

Dominant Negative ◽

Blastocyst Formation

ABSTRACT Blastocyst formation during mammalian preimplantation development is a unique developmental process that involves lineage segregation between the inner cell mass and the trophectoderm. To elucidate the molecular mechanisms underlying blastocyst formation, we have functionally screened a subset of preimplantation embryo-associated transcripts by using small interfering RNA (siRNA) and identified Bysl (bystin-like) as an essential gene for this process. The development of embryos injected with Bysl siRNA was arrested just prior to blastocyst formation, resulting in a defect in trophectoderm differentiation. Silencing of Bysl by using an episomal short hairpin RNA expression vector inhibited proliferation of embryonic stem cells. Exogenously expressed Bysl tagged with a fluorescent protein was concentrated in the nucleolus with a diffuse nucleoplasmic distribution. Furthermore, the loss of Bysl function by using RNA interference or dominant negative mutants caused defects in 40S ribosomal subunit biogenesis. These findings provide evidence for a crucial role of Bysl as an integral factor for ribosome biogenesis and suggest a critical dependence of blastocyst formation on active translation machinery.

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The Role of Zinc in Thyroid Hormones Metabolism

International Journal for Vitamin and Nutrition Research ◽

10.1024/0300-9831/a000262 ◽

2019 ◽

Vol 89 (1-2) ◽

pp. 80-88 ◽

Cited By ~ 6

Author(s):

Juliana Soares Severo ◽

Jennifer Beatriz Silva Morais ◽

Taynáh Emannuelle Coelho de Freitas ◽

Ana Letícia Pereira Andrade ◽

Mayara Monte Feitosa ◽

...

Keyword(s):

Thyroid Hormones ◽

Scientific Evidence ◽

Thyroid Stimulating Hormone ◽

Zinc Transporters ◽

Serum Concentrations ◽

Metabolic Adaptations ◽

Serum T3 ◽

Regulatory Effects ◽

Shed Light

Abstract. Thyroid hormones play an important role in body homeostasis by facilitating metabolism of lipids and glucose, regulating metabolic adaptations, responding to changes in energy intake, and controlling thermogenesis. Proper metabolism and action of these hormones requires the participation of various nutrients. Among them is zinc, whose interaction with thyroid hormones is complex. It is known to regulate both the synthesis and mechanism of action of these hormones. In the present review, we aim to shed light on the regulatory effects of zinc on thyroid hormones. Scientific evidence shows that zinc plays a key role in the metabolism of thyroid hormones, specifically by regulating deiodinases enzymes activity, thyrotropin releasing hormone (TRH) and thyroid stimulating hormone (TSH) synthesis, as well as by modulating the structures of essential transcription factors involved in the synthesis of thyroid hormones. Serum concentrations of zinc also appear to influence the levels of serum T3, T4 and TSH. In addition, studies have shown that Zinc transporters (ZnTs) are present in the hypothalamus, pituitary and thyroid, but their functions remain unknown. Therefore, it is important to further investigate the roles of zinc in regulation of thyroid hormones metabolism, and their importance in the treatment of several diseases associated with thyroid gland dysfunction.

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