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: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:Assembly factors play a critical role in the biogenesis of mitochondrial respiratory chain complexes I-IV where they assist in the membrane insertion of subunits, attachment of co-factors, and stabilization of assembly intermediates. The major fraction of complexes I, III and IV are present together in large molecular structures known as respiratory chain supercomplexes. A number of assembly factors have been proposed as required for supercomplex assembly, including the hypoxia inducible gene 1 domain family member HIGD2A. Using gene-edited human cell lines and extensive steady state, translation and affinity enrichment proteomics techniques we show that loss of HIGD2A leads to defects in the de novo biogenesis of mtDNA-encoded COX3, subsequent accumulation of complex IV intermediates and turnover of COX3 partner proteins. Deletion of HIGD2A also leads to defective complex IV activity. The impact of HIGD2A loss on complex IV was not altered by growth under hypoxic conditions, consistent with its role being in basal complex IV assembly. While in the absence of HIGD2A we show that mitochondria do contain an altered supercomplex assembly, we demonstrate it to harbor a crippled complex IV lacking COX3. Our results redefine HIGD2A as a classical assembly factor required for building the COX3 module of complex IV.
Project description:CRISPR-Cas mediated DNA-interference typically relies on sequence-specific binding and nucleolytic degradation of foreign genetic material. Type IV-A CRISPR-Cas systems diverge from this general mechanism, using a nuclease-independent interference pathway to suppress gene expression for gene regulation and plasmid competition. To understand how the type IV-A system associated effector complex achieves this interference, we determined cryo-EM structures of two evolutionarily distinct type IV-A complexes (types IV-38 A1 and IV-A3) bound to cognate DNA-targets in the presence and absence of the type IV-A signature DinG effector helicase. The structures reveal how the effector complexes recognize the protospacer adjacent motif and target-strand DNA to form an R-loop structure. Additionally, we reveal differences between types IV-A1 and IV-A3 in DNA interactions and structural motifs that allow for in trans recruitment of DinG. Our study provides a detailed view of type IV-A mediated DNA-interference and presents a structural foundation for engineering type IV-A-based genome editing tools.
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.