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https://www.readbyqxmd.com/read/28076289/from-bacteria-to-chloroplasts-evolution-of-the-chloroplast-srp-system
#1
Dominik Ziehe, Beatrix Dünschede, Danja Schünemann
Chloroplasts derive from a prokaryotic symbiont that lost most of its genes during evolution. As a result, the great majority of chloroplast proteins are encoded in the nucleus and are posttranslationally imported into the organelle. The chloroplast genome encodes only a few proteins. These include several multispan thylakoid membrane proteins which are synthesized on thylakoid-bound ribosomes and cotranslationally inserted into the membrane. During evolution, ancient prokaryotic targeting machineries were adapted and combined with novel targeting mechanisms to facilitate post- and cotranslational protein transport in chloroplasts...
January 10, 2017: Biological Chemistry
https://www.readbyqxmd.com/read/28067917/structural-insights-into-a-unique-hsp70-hsp40-interaction-in-the-eukaryotic-ribosome-associated-complex
#2
Felix Alexander Weyer, Andrea Gumiero, Genís Valentín Gesé, Karine Lapouge, Irmgard Sinning
Cotranslational chaperones assist de novo folding of nascent polypeptides, prevent them from aggregating and modulate translation. The ribosome-associated complex (RAC) is unique in that the Hsp40 protein Zuo1 and the atypical Hsp70 chaperone Ssz1 form a stable heterodimer, which acts as a cochaperone for the Hsp70 chaperone Ssb. Here we present the structure of the Chaetomium thermophilum RAC core comprising Ssz1 and the Zuo1 N terminus. We show how the conserved allostery of Hsp70 proteins is abolished and this Hsp70-Hsp40 pair is molded into a functional unit...
January 9, 2017: Nature Structural & Molecular Biology
https://www.readbyqxmd.com/read/27969102/regulation-evolution-and-consequences-of-cotranslational-protein-complex-assembly
#3
REVIEW
Eviatar Natan, Jonathan N Wells, Sarah A Teichmann, Joseph A Marsh
Most proteins assemble into complexes, which are involved in almost all cellular processes. Thus it is crucial for cell viability that mechanisms for correct assembly exist. The timing of assembly plays a key role in determining the fate of the protein: if the protein is allowed to diffuse into the crowded cellular milieu, it runs the risk of forming non-specific interactions, potentially leading to aggregation or other deleterious outcomes. It is therefore expected that strong regulatory mechanisms should exist to ensure efficient assembly...
December 12, 2016: Current Opinion in Structural Biology
https://www.readbyqxmd.com/read/27941902/protective-role-for-lipid-modifications-of-src-family-kinases-against-chromosome-missegregation
#4
Takuya Honda, Shuhei Soeda, Kunihiko Tsuda, Chihiro Yamaguchi, Kazumasa Aoyama, Takao Morinaga, Ryuzaburo Yuki, Yuji Nakayama, Noritaka Yamaguchi, Naoto Yamaguchi
Src-family tyrosine kinases, which are expressed in various cell types, play critical roles in cell signalling at the cytoplasmic side of the plasma membrane through their lipid modifications. Src-family kinases are cotranslationally myristoylated and posttranslationally palmitoylated in the amino-terminal region. The Src-family member Lyn contains a myristoylation site at glycine-2 and a palmitoylation site at cysteine-3, whereas c-Src has a myristoylation site at glycine-2 but not any palmitoylation sites...
December 12, 2016: Scientific Reports
https://www.readbyqxmd.com/read/27908229/localization-of-nuclear-encoded-mrnas-to-mitochondria-outer-surface
#5
REVIEW
A Golani-Armon, Y Arava
The diverse functions of mitochondria depend on hundreds of different proteins. The vast majority of these proteins is encoded in the nucleus, translated in the cytosol, and must be imported into the organelle. Import was shown to occur after complete synthesis of the protein, with the assistance of cytosolic chaperones that maintain it in an unfolded state and target it to the mitochondrial translocase of the outer membrane (TOM complex). Recent studies, however, identified many mRNAs encoding mitochondrial proteins near the outer membrane of mitochondria...
October 2016: Biochemistry. Biokhimii︠a︡
https://www.readbyqxmd.com/read/27895124/anionic-phospholipids-and-the-albino3-translocase-activate-signal-recognition-particle-receptor-interaction-during-light-harvesting-chlorophyll-a-b-binding-protein-targeting
#6
Sowmya Chandrasekar, Shu-Ou Shan
The universally conserved signal recognition particle (SRP) co-translationally delivers newly synthesized membrane and secretory proteins to the target cellular membrane. The only exception is found in the chloroplast of green plants, where the chloroplast SRP (cpSRP) post-translationally targets light-harvesting chlorophyll a/b-binding proteins (LHCP) to the thylakoid membrane. The mechanism and regulation of this post-translational mode of targeting by cpSRP remain unclear. Using biochemical and biophysical methods, here we show that anionic phospholipids activate the cpSRP receptor cpFtsY to promote rapid and stable cpSRP54·cpFtsY complex assembly...
January 6, 2017: Journal of Biological Chemistry
https://www.readbyqxmd.com/read/27882919/interaction-of-the-cotranslational-hsp70-ssb-with-ribosomal-proteins-and-rrna-depends-on-its-lid-domain
#7
Andrea Gumiero, Charlotte Conz, Genís Valentín Gesé, Ying Zhang, Felix Alexander Weyer, Karine Lapouge, Julia Kappes, Ulrike von Plehwe, Géza Schermann, Edith Fitzke, Tina Wölfle, Tamás Fischer, Sabine Rospert, Irmgard Sinning
Cotranslational chaperones assist in de novo folding of nascent polypeptides in all organisms. In yeast, the heterodimeric ribosome-associated complex (RAC) forms a unique chaperone triad with the Hsp70 homologue Ssb. We report the X-ray structure of full length Ssb in the ATP-bound open conformation at 2.6 Å resolution and identify a positively charged region in the α-helical lid domain (SBDα), which is present in all members of the Ssb-subfamily of Hsp70s. Mutational analysis demonstrates that this region is strictly required for ribosome binding...
November 24, 2016: Nature Communications
https://www.readbyqxmd.com/read/27881602/n-terminal-acetylation-promotes-synaptonemal-complex-assembly-in-c-elegans
#8
Jinmin Gao, Consuelo Barroso, Pan Zhang, Hyun-Min Kim, Shangtong Li, Leticia Labrador, James Lightfoot, Maxim V Gerashchenko, Vyacheslav M Labunskyy, Meng-Qiu Dong, Enrique Martinez-Perez, Monica P Colaiácovo
N-terminal acetylation of the first two amino acids on proteins is a prevalent cotranslational modification. Despite its abundance, the biological processes associated with this modification are not well understood. Here, we mapped the pattern of protein N-terminal acetylation in Caenorhabditis elegans, uncovering a conserved set of rules for this protein modification and identifying substrates for the N-terminal acetyltransferase B (NatB) complex. We observed an enrichment for global protein N-terminal acetylation and also specifically for NatB substrates in the nucleus, supporting the importance of this modification for regulating biological functions within this cellular compartment...
November 1, 2016: Genes & Development
https://www.readbyqxmd.com/read/27861610/the-chloroplast-srp-systems-of-chaetosphaeridium-globosum-and-physcomitrella-patens-as-intermediates-in-the-evolution-of-srp-dependent-protein-transport-in-higher-plants
#9
Dominik Ziehe, Beatrix Dünschede, Mira Zenker, Silke Funke, Marc M Nowaczyk, Danja Schünemann
The bacterial signal recognition particle (SRP) mediates the cotranslational targeting of membrane proteins and is a high affinity complex consisting of a SRP54 protein subunit (Ffh) and an SRP RNA. The chloroplast SRP (cpSRP) pathway has adapted throughout evolution to enable the posttranslational targeting of the light harvesting chlorophyll a/b binding proteins (LHCPs) to the thylakoid membrane. In spermatophytes (seed plants), the cpSRP lacks the SRP RNA and is instead formed by a high affinity interaction of the conserved 54-kD subunit (cpSRP54) with the chloroplast-specific cpSRP43 protein...
2016: PloS One
https://www.readbyqxmd.com/read/27828954/prion-associated-toxicity-is-rescued-by-elimination-of-cotranslational-chaperones
#10
Kathryn M Keefer, Heather L True
The nascent polypeptide-associated complex (NAC) is a highly conserved but poorly characterized triad of proteins that bind near the ribosome exit tunnel. The NAC is the first cotranslational factor to bind to polypeptides and assist with their proper folding. Surprisingly, we found that deletion of NAC subunits in Saccharomyces cerevisiae rescues toxicity associated with the strong [PSI+] prion. This counterintuitive finding can be explained by changes in chaperone balance and distribution whereby the folding of the prion protein is improved and the prion is rendered nontoxic...
November 2016: PLoS Genetics
https://www.readbyqxmd.com/read/27802322/the-selenocysteine-specific-elongation-factor-contains-unique-sequences-that-are-required-for-both-nuclear-export-and-selenocysteine-incorporation
#11
Aditi Dubey, Paul R Copeland
Selenocysteine (Sec) is a critical residue in at least 25 human proteins that are essential for antioxidant defense and redox signaling in cells. Sec is inserted into proteins cotranslationally by the recoding of an in-frame UGA termination codon to a Sec codon. In eukaryotes, this recoding event requires several specialized factors, including a dedicated, Sec-specific elongation factor called eEFSec, which binds Sec-tRNASec with high specificity and delivers it to the ribosome for selenoprotein production...
2016: PloS One
https://www.readbyqxmd.com/read/27795329/seca-cotranslationally-interacts-with-nascent-substrate-proteins-in-vivo
#12
Damon Huber, Mohammed Jamshad, Ruby Hanmer, Daniela Schibich, Kristina Döring, Isabella Marcomini, Günter Kramer, Bernd Bukau
: SecA is an essential component of the Sec machinery in bacteria, which is responsible for transporting proteins across the cytoplasmic membrane. Recent work from our laboratory indicates that SecA binds to ribosomes. Here, we used two different approaches to demonstrate that SecA also interacts with nascent polypeptides in vivo and that these polypeptides are Sec substrates. First, we photo-cross-linked SecA to ribosomes in vivo and identified mRNAs that copurify with SecA. Microarray analysis of the copurifying mRNAs indicated a strong enrichment for proteins containing Sec-targeting sequences...
January 15, 2017: Journal of Bacteriology
https://www.readbyqxmd.com/read/27746049/the-ribosome-as-a-platform-for-mrna-and-nascent-polypeptide-quality-control
#13
REVIEW
Toshifumi Inada
Accurate gene expression is a prerequisite for all cellular processes. Quality control machineries respond to errors during protein synthesis by refolding polypeptides or targeting them for degradation. As another layer of gene expression control, aberrant mRNAs can also be detected and eliminated by mRNA quality control systems while engaging the ribosome. In this review, I focus on recent studies on the cotranslational quality control mechanisms induced by abnormal translational elongation and termination, which result in the rapid degradation of aberrant polypeptides and mRNAs...
January 2017: Trends in Biochemical Sciences
https://www.readbyqxmd.com/read/27723196/rna-decay-systems-enhance-reciprocal-switching-of-sense-and-antisense-transcripts-in-response-to-glucose-starvation
#14
Atsuko Miki, Josephine Galipon, Satoshi Sawai, Toshifumi Inada, Kunihiro Ohta
Antisense RNA has emerged as a crucial regulator of opposite-strand protein-coding genes in the long noncoding RNA (lncRNA) category, but little is known about their dynamics and decay process in the context of a stress response. Antisense transcripts from the fission yeast fbp1 locus (fbp1-as) are expressed in glucose-rich conditions and anticorrelated with transcription of metabolic stress-induced lncRNA (mlonRNA) and mRNA on the sense strand during glucose starvation. Here, we investigate the localization and decay of antisense RNAs at fbp1 and other loci, and propose a model to explain the rapid switch between antisense and sense mlonRNA/mRNA transcription triggered by glucose starvation...
December 2016: Genes to Cells: Devoted to Molecular & Cellular Mechanisms
https://www.readbyqxmd.com/read/27684475/cell-free-systems-based-on-cho-cell-lysates-optimization-strategies-synthesis-of-difficult-to-express-proteins-and-future-perspectives
#15
Lena Thoring, Doreen A Wüstenhagen, Maria Borowiak, Marlitt Stech, Andrei Sonnabend, Stefan Kubick
Nowadays, biotechnological processes play a pivotal role in target protein production. In this context, Chinese Hamster Ovary (CHO) cells are one of the most prominent cell lines for the expression of recombinant proteins and revealed as a safe host for nearly 40 years. Nevertheless, the major bottleneck of common in vivo protein expression platforms becomes obvious when looking at the production of so called "difficult-to-express" proteins. This class of proteins comprises in particular several ion channels and multipass membrane proteins as well as cytotoxic proteins...
2016: PloS One
https://www.readbyqxmd.com/read/27669034/dual-interaction-of-the-hsp70-j-protein-cochaperone-zuotin-with-the-40s-and-60s-ribosomal-subunits
#16
Kanghyun Lee, Ruchika Sharma, Om Kumar Shrestha, Craig A Bingman, Elizabeth A Craig
Ribosome-associated J protein-Hsp70 chaperones promote nascent-polypeptide folding and normal translational fidelity. The J protein Zuo1 is known to span the ribosomal subunits, but understanding of its function is limited. Here we present new structural and cross-linking data allowing more precise positioning of Saccharomyces cerevisiae Zuo1 near the 60S polypeptide-exit site and suggesting interactions of Zuo1 with the ribosomal protein eL31 and 25S rRNA helix 24. The junction between the 60S-interacting and subunit-spanning helices is a hinge that positions Zuo1 on the 40S yet accommodates subunit rotation...
November 2016: Nature Structural & Molecular Biology
https://www.readbyqxmd.com/read/27601675/energetics-of-side-chain-snorkeling-in-transmembrane-helices-probed-by-nonproteinogenic-amino-acids
#17
Karin Öjemalm, Takashi Higuchi, Patricia Lara, Erik Lindahl, Hiroaki Suga, Gunnar von Heijne
Cotranslational translocon-mediated insertion of membrane proteins into the endoplasmic reticulum is a key process in membrane protein biogenesis. Although the mechanism is understood in outline, quantitative data on the energetics of the process is scarce. Here, we have measured the effect on membrane integration efficiency of nonproteinogenic analogs of the positively charged amino acids arginine and lysine incorporated into model transmembrane segments. We provide estimates of the influence on the apparent free energy of membrane integration (ΔGapp) of "snorkeling" of charged amino acids toward the lipid-water interface, and of charge neutralization...
September 20, 2016: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/27550809/the-ribosome-associated-mba1-escorts-cox2-from-insertion-machinery-to-maturing-assembly-intermediates
#18
Isotta Lorenzi, Silke Oeljeklaus, Christin Ronsör, Bettina Bareth, Bettina Warscheid, Peter Rehling, Sven Dennerlein
The three conserved core subunits of the cytochrome c oxidase are mitochondrial-encoded in close to all eukaryotes. The Cox2 subunit spans the inner membrane twice, exposing N- and C-terminus into the intermembrane space. For this the N-terminus is exported cotranslationally by Oxa1 and subsequently undergoes proteolytic maturation in Saccharomyces cerevisiae Little is known about the translocation of the C-terminus but Cox18 has been identified as a critical protein in this process. Here we find that the scaffold protein Cox20, which promotes processing of Cox2, is in complex with the ribosome-receptor Mba1 and translating mitochondrial ribosomes in a Cox2-dependent manner...
August 22, 2016: Molecular and Cellular Biology
https://www.readbyqxmd.com/read/27542228/metap1-and-metap2-drive-cell-selectivity-for-a-potent-anti-cancer-agent-in-synergy-by-controlling-glutathione-redox-state
#19
Frédéric Frottin, Willy V Bienvenut, Jérôme Bignon, Eric Jacquet, Alvaro Sebastian Vaca Jacome, Alain Van Dorsselaer, Sarah Cianferani, Christine Carapito, Thierry Meinnel, Carmela Giglione
Fumagillin and its derivatives are therapeutically useful because they can decrease cancer progression. The specific molecular target of fumagillin is methionine aminopeptidase 2 (MetAP2), one of the two MetAPs present in the cytosol. MetAPs catalyze N-terminal methionine excision (NME), an essential pathway of cotranslational protein maturation. To date, it remains unclear the respective contribution of MetAP1 and MetAP2 to the NME process in vivo and why MetAP2 inhibition causes cell cycle arrest only in a subset of cells...
September 27, 2016: Oncotarget
https://www.readbyqxmd.com/read/27487213/cotranslational-signal-independent-srp-preloading-during-membrane-targeting
#20
Justin W Chartron, Katherine C L Hunt, Judith Frydman
Ribosome-associated factors must properly decode the limited information available in nascent polypeptides to direct them to their correct cellular fate. It is unclear how the low complexity information exposed by the nascent chain suffices for accurate recognition by the many factors competing for the limited surface near the ribosomal exit site. Questions remain even for the well-studied cotranslational targeting cycle to the endoplasmic reticulum, involving recognition of linear hydrophobic signal sequences or transmembrane domains by the signal recognition particle (SRP)...
August 11, 2016: Nature
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