Reconstitution into liposomes of membrane proteins involved in ribosome binding on rough endoplasmic reticulum. Ribosome-binding capacity.
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ABSTRACT:
SUBMITTER: Yamaguchi M
PROVIDER: S-EPMC1162827 | biostudies-other | 1981 Mar
REPOSITORIES: biostudies-other
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Project description:A membrane protein fraction showing affinity for ribosomes was isolated from rat liver microsomes (microsomal fractions) in association with ribosomes by treatment of the microsomes with Emulgen 913 and then solubilized from the ribosomes with sodium deoxycholate. This protein fraction was separated into two fractions, glycoproteins, including ribophorins I and II, and non-glycoproteins, virtually free from ribophorins I and II, on concanavalin A-Sepharose columns. The two fractions were each reconstituted into liposomes to determine their ribosome-binding activities. The specific binding activity of the non-glycoprotein fraction was approx. 2.3-fold higher than that of the glycoprotein fraction. The recovery of ribosome-binding capacity of the two fractions was about 85% of the total binding capacity of the material applied to a concanavalin A-Sepharose column, and about 90% of it was found in the non-glycoprotein fraction. The affinity constants of the ribosomes for the reconstituted liposomes were somewhat higher than those for stripped rough microsomes. The mode of ribosome binding to the reconstituted liposomes was very similar to that to the stripped rough microsomes, in its sensitivity to proteolytic enzymes and its strong inhibition by increasing KCl concentration. These results support the idea that ribosome binding to rat liver microsomes is not directly mediated by ribophorins I and II, but that another unidentified membrane protein(s) plays a role in ribosome binding.
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Project description:Aim and experimental set-up: Sequencing of small RNA from total RNA fractions. The aim of this experiment was to compare profiles of miRNA expression between the following genetic backgrounds: Col-0 (wild type), era1-2 (farnesyl transferase mutant), j2-2/j3-2 + pJ3:J3 (j2/j3 double knockout expressing transgenic J3 under the control of the endogenous J3 promoter), j2-2/j3-2 + pJ3:J3C417S (j2/j3 double knockout expressing transgenic J3 mutated in the farnesylation site (C417S) under the control of the endogenous J3 promoter). Seedlings were grown under sterile conditions for 16 days. Two biological replicates of each genotype were harvested, and total RNA was prepared by Trizol extraction. Small RNA libraries were constructed using NEBNext Small RNA Library Prep Set and sequenced on an Illumina platform. Sequencing of small RNA bound to AGO1 in membrane fractions The aim of this experiment was to characterize AGO1-bound small RNAs in membrane fractions, and to answer two specific questions: Can miRNAs be identified whose association with membrane-bound AGO1 is different between the following four genotypes: Col-0 (wild type), era1-2 (farnesyl transferase mutant), j2-2/j3-2 + pJ3:J3 (j2/j3 double knockout expressing transgenic J3 under the control of the endogenous J3 promoter), j2-2/j3-2 + pJ3:J3C417S (j2/j3 double knockout expressing transgenic J3 mutated in the farnesylation site (C417S) under the control of the endogenous J3 promoter) Is the ratio between reads matching miRNA and miRNA* different between the above four genotypes? Seedlings were grown under sterile conditions for 16 days. Two biological replicates of each genotype were harvested. Microsomes were prepared from 2g of seedling tissue, solubilized by 1% deoxycholate and AGO1 was immunoprecipitated with specific antibodies (Agrisera). Immunopurified AGO1 was eluted from Protein A sepharose beads by competitive elution with antigenic AGO1 peptide. Small RNA was extracted by Trizol extraction from eluted AGO1. Small RNA libraries were constructed using NEBNext Small RNA Library Prep Set and sequenced on an Illumina platform.
2016-07-31 | E-MTAB-3736 | biostudies-arrayexpress
Project description:We have addressed how ribosome-nascent chain complexes (RNCs), associated with the signal recognition particle (SRP), can be targeted to Sec61 translocation channels of the endoplasmic reticulum (ER) membrane when all binding sites are occupied by nontranslating ribosomes. These competing ribosomes are known to be bound with high affinity to tetramers of the Sec61 complex. We found that the membrane binding of RNC-SRP complexes does not require or cause the dissociation of prebound nontranslating ribosomes, a process that is extremely slow. SRP and its receptor target RNCs to a free population of Sec61 complex, which associates with nontranslating ribosomes only weakly and is conformationally different from the population of ribosome-bound Sec61 complex. Taking into account recent structural data, we propose a model in which SRP and its receptor target RNCs to a Sec61 subpopulation of monomeric or dimeric state. This could explain how RNC-SRP complexes can overcome the competition by nontranslating ribosomes.
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Project description:In vitro the binding of polyribosomes to smooth endoplasmic-reticulum membranes is more sensitive to ionic strength than is the binding to rough endoplasmic-reticulum membranes. Polyribosomes from the free and membrane-bound fractions bind with equal efficiency to endoplasmic-reticulum membranes.
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Project description:Pancreatic beta cells have well-developed ER to accommodate for the massive production and secretion of insulin. ER homeostasis is vital for normal beta cell function. Perturbation of ER homeostasis contributes to beta cell dysfunction in both type 1 and type 2 diabetes. To systematically identify the molecular machinery responsible for proinsulin biogenesis and maintenance of beta cell ER homeostasis, a widely used mouse pancreatic beta cell line, MIN6 cell was used to purify rough ER. Two different purification schemes were utilized. In each experiment, the ER pellets were solubilized and analyzed by 1D SDS-PAGE coupled with HPLC-MS/MS. A total of 1467 proteins were identified in three experiments with ?95% confidence, among which 1117 proteins were found in at least two separate experiments and 737 proteins found in all three experiments. GO analysis revealed a comprehensive profile of known and novel players responsible for proinsulin biogenesis and ER homeostasis. Further bioinformatics analysis also identified potential beta cell specific ER proteins as well as ER proteins present in the risk genetic loci of type 2 diabetes. This dataset defines a molecular environment in the ER for proinsulin synthesis, folding and export and laid a solid foundation for further characterizations of altered ER homeostasis under diabetes-causing conditions. All MS data have been deposited in the ProteomeXchange with identifier PXD001081 (http://proteomecentral.proteomexchange.org/dataset/PXD001081).
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Project description:Molecular mechanisms underlying Ca(2+) regulation by perinuclear endoplasmic/sarcoplasmic reticulum (ER/SR) cisternae in cardiomyocytes remain obscure. To investigate the mechanisms of changes in cardiac calsequestrin (CSQ2) trafficking on perinuclear Ca(2+) signaling, we manipulated the subcellular distribution of CSQ2 by overexpression of CSQ2-DsRed, which specifically accumulates in the perinuclear rough ER. Adult ventricular myocytes were infected with adenoviruses expressing CSQ2-DsRed, CSQ2-WT, or empty vector. We found that perinuclear enriched CSQ2-DsRed, but not normally distributed CSQ2-WT, enhanced nuclear Ca(2+) transients more potently than cytosolic Ca(2+) transients. Overexpression of CSQ2-DsRed produced more actively propagating Ca(2+) waves from perinuclear regions than did CSQ2-WT. Activities of the SR/ER Ca(2+)-ATPase and ryanodine receptor type 2, but not inositol 1,4,5-trisphosphate receptor type 2, were required for the generation of these perinuclear initiated Ca(2+) waves. In addition, CSQ2-DsRed was more potent than CSQ2-WT in inducing cellular hypertrophy in cultured neonatal cardiomyocytes. Our data demonstrate for the first time that CSQ2 retention in the rough ER/perinuclear region promotes perinuclear Ca(2+) signaling and predisposes to ryanodine receptor type 2-mediated Ca(2+) waves from CSQ2-enriched perinuclear compartments and myocyte hypotrophy. These findings provide new insights into the mechanism of CSQ2 in Ca(2+) homeostasis, suggesting that rough ER-localized Ca(2+) stores can operate independently in raising levels of cytosolic/nucleoplasmic Ca(2+) as a source of Ca(2+) for Ca(2+)-dependent signaling in health and disease.
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Project description:In eukaryotic cells, the spatial regulation of protein expression is frequently conferred through the coupling of mRNA localization and the local control of translation. mRNA localization to the endoplasmic reticulum (ER) is a prominent example of such regulation and serves a ubiquitous role in segregating the synthesis of secretory and integral membrane proteins to the ER. Recent genomic and biochemical studies have now expanded this view to suggest a role for the ER in global protein synthesis. We have utilized cell fractionation and ribosome profiling to obtain a genomic survey of the subcellular organization of mRNA translation and report that ribosomal loading of mRNAs, a proxy for mRNA translation, is biased to the ER. Notably, ER-associated mRNAs encoding both cytosolic and topogenic signal-encoding proteins display similar ribosome loading densities, suggesting that ER-associated ribosomes serve a global role in mRNA translation. We propose that the partitioning of mRNAs and their translation between the cytosol and ER compartments may represent a novel mechanism for the post-transcriptional regulation of gene expression. HEK293 cells were fractionated between the cytosol and endoplasmic reticulum. Within each fraction, ribosome footprints were generated and sequenced. In parallel, total mRNA was sequenced.
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