Isolation of mitochondria from Saccharomyces cerevisiae using magnetic bead affinity purification

Long-read direct RNA sequencing of the mitochondrial transcriptome of Saccharomyces cerevisiae reveals condition-dependent intron abundance

Mitochondria fulfil many essential roles and have their own genome, which is expressed as polycistronic transcripts that undergo co- or posttranscriptional processing and splicing. Due to the inherent complexity and limited technical accessibility of the mitochondrial transcriptome, fundamental questions regarding mitochondrial gene expression and splicing remain unresolved, even in the model eukaryote Saccharomyces cerevisiae. Long-read sequencing could address these fundamental questions. Therefore, a method for the enrichment of mitochondrial RNA and sequencing using Nanopore technology was developed, enabling the resolution of splicing of polycistronic genes and the quantification of spliced RNA. This method successfully captured the full mitochondrial transcriptome and resolved RNA splicing patterns with single-base resolution and was applied to explore the transcriptome of S. cerevisiae grown with glucose or ethanol as the sole carbon source, revealing the impact of growth conditions on mitochondrial RNA expression and splicing. This study uncovered a remarkable difference in the turnover of Group II introns between yeast grown in either mostly fermentative or fully respiratory conditions. Whether this accumulation of introns in glucose medium has an impact on mitochondrial functions remains to be explored. Combined with the high tractability of the model yeast S. cerevisiae, the developed method enables to monitor mitochondrial transcriptome responses in a broad range of relevant contexts, including oxidative stress, apoptosis and mitochondrial diseases.

Mitochondria in disease: changes in shapes and dynamics

Mitochondrial structure often determines the function of these highly dynamic, multifunctional, eukaryotic organelles, which are essential for maintaining cellular health. The dynamic nature of mitochondria is apparent in descriptions of different mitochondrial shapes [e.g., donuts, megamitochondria (MGs), and nanotunnels] and crista dynamics. This review explores the significance of dynamic alterations in mitochondrial morphology and regulators of mitochondrial and cristae shape. We focus on studies across tissue types and also describe new microscopy techniques for detecting mitochondrial morphologies both in vivo and in vitro that can improve understanding of mitochondrial structure. We highlight the potential therapeutic benefits of regulating mitochondrial morphology and discuss prospective avenues to restore mitochondrial bioenergetics to manage diseases related to mitochondrial dysfunction.

MemPrep, a new technology for isolating organellar membranes provides fingerprints of lipid bilayer stress

Biological membranes have a stunning ability to adapt their composition in response to physiological stress and metabolic challenges. Little is known how such perturbations affect individual organelles in eukaryotic cells. Pioneering work has provided insights into the subcellular distribution of lipids in the yeast Saccharomyces cerevisiae, but the composition of the endoplasmic reticulum (ER) membrane, which also crucially regulates lipid metabolism and the unfolded protein response, remains insufficiently characterized. Here, we describe a method for purifying organelle membranes from yeast, MemPrep. We demonstrate the purity of our ER membrane preparations by proteomics, and document the general utility of MemPrep by isolating vacuolar membranes. Quantitative lipidomics establishes the lipid composition of the ER and the vacuolar membrane. Our findings provide a baseline for studying membrane protein biogenesis and have important implications for understanding the role of lipids in regulating the unfolded protein response (UPR). The combined preparative and analytical MemPrep approach uncovers dynamic remodeling of ER membranes in stressed cells and establishes distinct molecular fingerprints of lipid bilayer stress.

Cellular organelles as drug carriers for disease treatment

Organelles not only constitute the basic structure of the cell but also are important in maintaining the normal physiological activities of the cell. With the development of biomimetic nanoscience, researchers have developed technologies to use organelles as drug carriers for disease treatment. Compared with traditional drug carriers, organelle drug carriers have the advantages of good biocompatibility, high drug loading efficiency, and modifiability, and the surface biomarkers of organelles can also participate in intracellular signal transduction to enhance intracellular and intercellular communication, and assist in enhancing the therapeutic effect of drugs. Among different types of organelles, extracellular vesicles, lipid droplets, lysosomes, and mitochondria have been used as drug carriers. This review briefly reviews the biogenesis, isolation methods, and drug-loading methods of four types of organelles, and systematically summarizes the research progress in using organelles as drug-delivery systems for disease treatment. Finally, the challenges faced by organelle-based drug delivery systems are discussed. Although the organelle-based drug delivery systems still face challenges before they can achieve clinical translation, they offer a new direction and vision for the development of next-generation drug carriers.

A method for isolating highly purified and active mitochondria from insects

So far, methods that yield the high purity and activity of the isolated mitochondria from insects have not been reported and determined. Here, we develop methods that combine differential centrifugation and discontinuous Nycodenz density gradient centrifugation to isolate highly purified mitochondria from the thorax muscle of insects, and the methods were widely validated across three orders (Coleoptera, Hymenoptera, and Blattaria) covering four insect species using Western blot and transmission electron microscopy (TEM) analysis. The results showed the removal of the residual contamination with nonmitochondrial components such as nucleus, sarcolemma, cytosol, and endoplasmic reticulum. Furthermore, TEM, mitochondria staining, fluorescence detection, and flow cytometry analyses were employed to assess membrane integrity and activity of the isolated mitochondria. The results showed no loss of mitochondria activity/integrity after isolation. In addition, temporal dynamics in activity of the isolated mitochondria under commonly used laboratory temperature (-20 °C, 4 °C, and 25 °C) were respectively detected using a fluorescence microplate reader. The results showed that it should be avoided to store the isolated mitochondria at room temperature, and the mitochondria can meet the requirements of the most downstream experiments when they were stored at -20 °C. Overall, the study presented a method for isolating highly purified and active mitochondria from insects. This study firstly described a high-speed discontinuous density gradient centrifugation-based method that could be widely applied for mitochondria isolation in insects. The present study also provided an example to assess purity and integrity/activity of the isolated mitochondria.

A Three-Dimensional Printed Inertial Microfluidic Platform for Isolation of Minute Quantities of Vital Mitochondria

We demonstrate a fast and easy-to-use three-dimensional printed microfluidic platform for mitochondria isolation from cell and tissue lysates based on inertial microfluidics. We present and quantify the quality of the isolated mitochondria by measuring the respiration rate under various conditions. We demonstrate that the technology produces vital mitochondria of equal quality to traditional, but more burdensome, differential centrifugation. We anticipate that the availability of improved tools for studies of bioenergetics to the broader biological community will enable these and other links to be explored in more meaningful ways, leading to further understanding of the links between energy, health, and disease.

Biomimetic Nanoparticles Enabled by Cascade Cell Membrane Coating for Direct Cross-Priming of T Cells

Despite the activation of T lymphocytes by antigen-presenting cells being responsible for eliciting antigen-specific immune responses, their crosstalking suffers from temporospatial limitations and endogenous influencing factors, which restrict the generation of a strong antitumor immunity. Here, cascade cell membrane coating is reported to prepare biomimetic nanoparticles (BNs) that can manipulate the cross-priming of T cells. BNs are obtained from coating nanoparticulate substrates with cell membranes extracted from dendritic cells (DCs) that are pre-pulsed with cancer cell membrane-coated nanoparticles. With a DC membrane that presents an array of cancer cell membrane antigen epitopes, BNs inherit the intrinsic membrane function of DCs, which can directly cross-prime T cells and provoke robust yet antigen-specific antitumor responses in multiple mouse models. Combination with clinical anti-programmed death-1 antibodies demonstrates a robust way of BNs to achieve desirable tumor regression and survival rate. This work spotlights the impact of nanoparticles on direct cross-priming of T cells and supports a unique yet modulate platform for boosting an effective adaptive immunity for immunotherapy.

In Vivo Epitope Tagging of Plant Mitochondria

Mitochondria play a key role in cellular metabolism. Analyses of the genome, the proteome, metabolic, physiological, and biochemical functions of mitochondria frequently require the isolation of intact and functional mitochondria from various plant tissues with sufficient yield. For this purpose, we generated a transgenic Arabidopsis thaliana (Arabidopsis) line which presents a triple hemagglutinin tag on the surface of the outer mitochondrial membrane. The affinity tag enables immunocapture of the organelles in a single step. This chapter gives detailed instructions on how to generate transgenic Arabidopsis lines harboring a ubiquitously expressed 3xHA-sGFP-TOM5 mitochondrial fusion protein that is targeted to the outer mitochondrial membrane and enables purification of the organelles in a single step.

Mitochondria-Associated Degradation Pathway (MAD) Function beyond the Outer Membrane

The mitochondria-associated degradation pathway (MAD) mediates ubiquitination and degradation of mitochondrial outer membrane (MOM) proteins by the proteasome. We find that the MAD, but not other quality-control pathways including macroautophagy, mitophagy, or mitochondrial chaperones and proteases, is critical for yeast cellular fitness under conditions of paraquat (PQ)-induced oxidative stress in mitochondria. Specifically, inhibition of the MAD increases PQ-induced defects in growth and mitochondrial quality and decreases chronological lifespan. We use mass spectrometry analysis to identify possible MAD substrates as mitochondrial proteins that exhibit increased ubiquitination in response to PQ treatment and inhibition of the MAD. We identify candidate substrates in the mitochondrial matrix and inner membrane and confirm that two matrix proteins are MAD substrates. Our studies reveal a broader function for the MAD in mitochondrial protein surveillance beyond the MOM and a major role for the MAD in cellular and mitochondrial fitness in response to chronic, low-level oxidative stress in mitochondria.

In vivo mRNA display enables large-scale proteomics by next generation sequencing

Large-scale proteomic methods are essential for the functional characterization of proteins in their native cellular context. However, proteomics has lagged far behind genomic approaches in scalability, standardization, and cost. Here, we introduce in vivo mRNA display, a technology that converts a variety of proteomics applications into a DNA sequencing problem. In vivo-expressed proteins are coupled with their encoding messenger RNAs (mRNAs) via a high-affinity stem-loop RNA binding domain interaction, enabling high-throughput identification of proteins with high sensitivity and specificity by next generation DNA sequencing. We have generated a high-coverage in vivo mRNA display library of the Saccharomyces cerevisiae proteome and demonstrated its potential for characterizing subcellular localization and interactions of proteins expressed in their native cellular context. In vivo mRNA display libraries promise to circumvent the limitations of mass spectrometry-based proteomics and leverage the exponentially improving cost and throughput of DNA sequencing to systematically characterize native functional proteomes.

MASS SPECTROMETRY-BASED MITOCHONDRIAL PROTEOMICS IN HUMAN OVARIAN CANCERS

The prominent characteristics of mitochondria are highly dynamic and regulatory, which have crucial roles in cell metabolism, biosynthetic, senescence, apoptosis, and signaling pathways. Mitochondrial dysfunction might lead to multiple serious diseases, including cancer. Therefore, identification of mitochondrial proteins in cancer could provide a global view of tumorigenesis and progression. Mass spectrometry-based quantitative mitochondrial proteomics fulfils this task by enabling systems-wide, accurate, and quantitative analysis of mitochondrial protein abundance, and mitochondrial protein posttranslational modifications (PTMs). Multiple quantitative proteomics techniques, including isotope-coded affinity tag, stable isotope labeling with amino acids in cell culture, isobaric tags for relative and absolute quantification, tandem mass tags, and label-free quantification, in combination with different PTM-peptide enrichment methods such as TiO₂ enrichment of tryptic phosphopeptides and antibody enrichment of other PTM-peptides, increase flexibility for researchers to study mitochondrial proteomes. This article reviews isolation and purification of mitochondria, quantitative mitochondrial proteomics, quantitative mitochondrial phosphoproteomics, mitochondrial protein-involved signaling pathway networks, mitochondrial phosphoprotein-involved signaling pathway networks, integration of mitochondrial proteomic and phosphoproteomic data with whole tissue proteomic and transcriptomic data and clinical information in ovarian cancers (OC) to in-depth understand its molecular mechanisms, and discover effective mitochondrial biomarkers and therapeutic targets for predictive, preventive, and personalized treatment of OC. This proof-of-principle model about OC mitochondrial proteomics is easily implementable to other cancer types. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Bead based facile assay for sensitive quantification of native state green fluorescent protein

A facile method for the quantification of native state protein is strongly required to accurately determine the amount of expressed protein of interest. Here we report a simple bead-based assay, which can sensitively quantify the amount of native state green fluorescent protein using Ni-NTA (nickel-nitrilotriacetic acid)-modified microbead particles. The bead-based method is simple and straightforward to perform and it showed a highly sensitive capability to detect the expressed fluorescent protein because of the enriched fluorescent protein on the beads.

Isolation of mitochondria from cells and tissues

Isolated mitochondria are useful to study fundamental processes including mitochondrial respiration, metabolic activity, protein import, membrane fusion, protein complex assembly, as well as interactions of mitochondria with the cytoskeleton, nuclear encoded mRNAs, and other organelles. In addition, studies of the mitochondrial proteome, phosphoproteome, and lipidome are dependent on preparation of highly purified mitochondria (Boldogh, Vojtov, Karmon, & Pon, 1998; Cui, Conte, Fox, Zara, & Winge, 2014; Marc et al., 2002; Meeusen, McCaffery, & Nunnari, 2004; Reinders et al., 2007; Schneiter et al., 1999; Stuart & Koehler, 2007). Most methods to isolate mitochondria rely on differential centrifugation, a two-step centrifugation carried out at low speed to remove intact cells, cell and tissue debris, and nuclei from whole cell extracts followed by high speed centrifugation to concentrate mitochondria and separate them from other organelles. However, methods to disrupt cells and tissue vary. Moreover, density gradient centrifugation or affinity purification of the organelle are used to further purify mitochondria or to separate different populations of the organelle. Here, we describe protocols to isolate mitochondria from different cells and tissues as well as approaches to assess the purity and integrity of isolated organelles.