Project description:Pulse (P) - Chase (C) SILAC analysis of mitochondrial complex assembly
Bogenhagen et al (2018) Cell Reports
Pulse-chase times in hours (P#C#)
Project description:We developed a simple method that combined biochemical mitochondria isolation and pulse SILAC approach to monitor the mitochondrial translation. Our approach allows us to quantify 12 out of the 13 mitochondrial translation products, the highest coverage among analogous methods reported, and provide a global picture of (post-)translational regulation in mitochondria. Replicate 1: H-CRP_M-DMSO, Replicate 2: M-CRP_H-DMSO.
Project description:Mitochondrial ribosomes are specialized to translate the 13 membrane proteins encoded in the mitochondrial genome, which shapes the oxidative phosphorylation complexes essential for cellular energy metabolism. Despite the importance of mitochondrial translation (MT) control, it is challenging to identify and quantify the mitochondrial-encoded proteins because of their hydrophobic nature and low abundance. Here, we introduce a mass spectrometry-based proteomic method that combines biochemical isolation of mitochondria with pulse stable isotope labeling by amino acids in cell culture. Our method provides the highest protein identification rate with the shortest measurement time among currently available methods, enabling us to quantify 12 of the 13 mitochondrial-encoded proteins. We applied this method to uncover the global picture of (post-)translational regulation of both mitochondrial- and nuclear-encoded subunits of oxidative phosphorylation complexes. We found that inhibition of MT led to degradation of orphan nuclear-encoded subunits that are considered to form subcomplexes with the mitochondrial-encoded subunits. This method should be readily applicable to study MT programs in many contexts, including oxidative stress and mitochondrial disease.
Project description:Pulse chase SILAC was used to identify protein turnover within human macrophages infected with mycobacterium tuberculosis CDC1551, a ppe38-71 mutant strain, a complemented strain and an uninfected control.
Project description:Manassantin A is a natural product that has been isolated from the perennial herb Saururus chinensis Baill and the aquatic plant Saururus cernuus. Manassantin A has been shown to possess potent hypoxia inducible factor 1 alpha (HIF-1α) inhibitory activity in a cell-based assay screen of thousands of natural products. Manassantin A holds promise as an anti-cancer drug since it has been shown to selectively target tumor cells over normal cells. Due to the complex biological pathways involved in cancer and hypoxia, it is difficult to determine the mode-of-action by which manassantin A inhibits HIF-1. While some of the biological activities of manassantin A have been discovered in various cell-based activity assays, the molecular basis of manassantin A’s biological activities is not well characterized. The proteins in a hypoxic MDA-MB-231 cell lysate were screened for interactions with manassantin A using large scale experiments to uncover novel manassantin A interactions that lead to the drug’s HIF-1 inhibition and anti-cancer activity. Two energetics-based approaches were utilized in this manassantin A mode-of-action study: iTRAQ-SPROX and SILAC-Pulse Proteolysis. In these energetics-based approaches, protein stability is measured using the chemical denaturant dependence of either a methionine oxidation reaction (iTRAQ-SPROX) or a thermolysin protease digest (SILAC-Pulse Proteolysis). Using boh of these techniques, the stability of proteins in the absence and presence of excess manassantin A was monitored to assess ligand-induced protein stability changes.
Project description:Mammalian mitochondria assemble four complexes of the respiratory chain (RCI, RCIII, RCIV, and RCV) by combining 13 polypeptides synthesized within mitochondria on mitochondrial ribosomes (mitoribosomes) with over 70 polypeptides encoded in nuclear DNA, translated on cytoplasmic ribosomes, and imported into mitochondria. We have previously observed that mitoribosome assembly is inefficient because some mitoribosomal proteins are produced in excess, but whether this is the case for other mitochondrial assemblies such as the RCs is unclear. We report here that pulse-chase stable isotope labeling with amino acids in cell culture (SILAC) is a valuable technique to study RC assembly because it can reveal considerable differences in the assembly rates and efficiencies of the different complexes. The SILAC analyses of HeLa cells indicated that assembly of RCV, comprising F1/Fo-ATPase, is rapid with little excess subunit synthesis, but that assembly of RCI (i.e. NADH dehydrogenase) is far less efficient, with dramatic oversynthesis of numerous proteins, particularly in the matrix-exposed N and Q domains. Unassembled subunits were generally degraded within 3 h. We also observed differential assembly kinetics for individual complexes that were immunoprecipitated with complex-specific antibodies. Immunoprecipitation with an antibody that recognizes the ND1 subunit of RCI co-precipitated a number of proteins implicated in FeS cluster assembly and newly synthesized ubiquinol-cytochrome c reductase Rieske iron-sulfur polypeptide 1 (UQCRFS1), the Rieske FeS protein in RCIII, reflecting some coordination between RCI and RCIII assemblies. We propose that pulse-chase SILAC labeling is a useful tool for studying rates of protein complex assembly and degradation.
Project description:In plants, the maintenance of DNA methylation is controlled by several self-reinforcing loops involving histone methylation and non-coding RNAs. However, how methylation is initially patterned at specific genomic loci is largely unknown. Here, we describe four Arabidopsis REM transcription factors, VDD, VAL, REM12 and REM13, that recognize specific sequence regions, and together with the protein GENETICS DETERMINES EPIGENETICS1 (GDE1), recruit RNA polymerase IV transcription complexes. This targeted recruitment leads to the production of 24-nucleotide small interfering RNAs (24nt-siRNAs) that guide DNA methylation to specific genomic sites in plant female reproductive tissues. In the absence of GDE1, Pol IV transcription complexes are directed to loci bound by an alternative transcription factor, REM8, highlighting the role of REM transcription factors and GDE1 proteins as positional cues for epigenetic modulation. These findings establish a direct connection between sequence-specific transcription factors and the spatial regulation of siRNAs production and DNA methylation, offering new insights into the genetic control of epigenetic patterning.
Project description:Accurate and efficient folding of nascent protein sequences into their native state requires support from the protein homeostasis network. Herein we probed which newly translated proteins are thermo-sensitive to infer which polypeptides require more time to fold within the proteome. Specifically, we determined which of these proteins were more susceptible to misfolding and aggregation under heat stress using pulse SILAC coupled mass spectrometry. These proteins are abundant, short, and highly structured. Notably these proteins display a tendency to form β-sheet secondary structures, a configuration which typically requires more time for folding, and were enriched for Hsp70/Ssb and TRiC/CCT binding motifs, suggesting a higher demand for chaperone-assisted folding. These polypeptides were also more often components of stable protein complexes in comparison to other proteins. Combining this evidence suggests that a specific subset of newly translated proteins in the cell requires more time following synthesis to reach a state less prone to aggregation upon stress.