Functional crosstalk between the TIM22 complex and YME1 machinery maintains mitochondrial proteostasis and integrity

Seahorse assay for the analysis of mitochondrial respiration using Saccharomyces cerevisiae as a model system

Eukaryotic cells require energy to perform diverse cellular functions critical for survival. Mitochondria are multifunctional organelles that generate energy in the form of Adenosine triphosphate by oxidative phosphorylation, emphasizing their importance to eukaryotic cell viability. The ability of mitochondria to consume oxygen for respiration is a key parameter in assessing mitochondrial health. Therefore, developing new techniques to monitor mitochondrial respiration are crucial for advancing our understanding of organelle functioning. Recently, Seahorse technology has emerged as a valuable tool to analyze various aspects of mitochondrial bioenergetics. Although the Seahorse assay is well established in adherent cell lines and other model organisms, it remains challenging to employ it efficiently in yeast, a powerful genetic system for studying mitochondrial biology. In this chapter, we provide a comprehensive methodology for assessing oxygen consumption rate in baker's yeast using Seahorse.

Mitochondrial complexome and import network

Mitochondria perform crucial functions in cellular metabolism, protein and lipid biogenesis, quality control, and signaling. The systematic analysis of protein complexes and interaction networks provided exciting insights into the structural and functional organization of mitochondria. Most mitochondrial proteins do not act as independent units, but are interconnected by stable or dynamic protein-protein interactions. Protein translocases are responsible for importing precursor proteins into mitochondria and form central elements of several protein interaction networks. These networks include molecular chaperones and quality control factors, metabolite channels and respiratory chain complexes, and membrane and organellar contact sites. Protein translocases link the distinct networks into an overarching network, the mitochondrial import network (MitimNet), to coordinate biogenesis, membrane organization and function of mitochondria.

Role of Yme1 in mitochondrial protein homeostasis: from regulation of protein import, OXPHOS function to lipid synthesis and mitochondrial dynamics

Mitochondria are essential organelles of eukaryotic cells and thus mitochondrial proteome is under constant quality control and remodelling. Yme1 is a multi-functional protein and subunit of the homo-hexametric complex i-AAA proteinase. Yme1 plays vital roles in the regulation of mitochondrial protein homeostasis and mitochondrial plasticity, ranging from substrate degradation to the regulation of protein functions involved in mitochondrial protein biosynthesis, energy production, mitochondrial dynamics, and lipid biosynthesis and signalling. In this mini review, we focus on discussing the current understanding of the roles of Yme1 in mitochondrial protein import via TIM22 and TIM23 pathways, oxidative phosphorylation complex function, as well as mitochondrial lipid biosynthesis and signalling, as well as a brief discussion of the role of Yme1 in modulating mitochondrial dynamics.

Mitochondria in biology and medicine - 2023

Mitochondria are an indispensable part of the cell that plays a crucial role in regulating various signaling pathways, energy metabolism, cell differentiation, proliferation, and cell death. Since mitochondria have their own genetic material, they differ from their nuclear counterparts, and dysregulation is responsible for a broad spectrum of diseases. Mitochondrial dysfunction is associated with several disorders, including neuro-muscular disorders, cancer, and premature aging, among others. The intricacy of the field is due to the cross-talk between nuclear and mitochondrial genes, which has also improved our knowledge of mitochondrial functions and their pathogenesis. Therefore, interdisciplinary research and communication are crucial for mitochondrial biology and medicine due to the challenges they pose for diagnosis and treatment. The ninth annual conference of the Society for Mitochondria Research and Medicine (SMRM)- India, titled "Mitochondria in Biology and Medicine" was organized at the Centre for DNA Fingerprinting and Diagnostics (CDFD), Hyderabad, India, on June 21-23, 2023. The latest advancements in the field of mitochondrial biology and medicine were discussed at the conference. In this article, we summarize the entire event for the benefit of researchers working in the field of mitochondrial biology and medicine.

Mitochondrial protein import clogging as a mechanism of disease

Mitochondrial biogenesis requires the import of >1,000 mitochondrial preproteins from the cytosol. Most studies on mitochondrial protein import are focused on the core import machinery. Whether and how the biophysical properties of substrate preproteins affect overall import efficiency is underexplored. Here, we show that protein traffic into mitochondria can be disrupted by amino acid substitutions in a single substrate preprotein. Pathogenic missense mutations in ADP/ATP translocase 1 (ANT1), and its yeast homolog ADP/ATP carrier 2 (Aac2), cause the protein to accumulate along the protein import pathway, thereby obstructing general protein translocation into mitochondria. This impairs mitochondrial respiration, cytosolic proteostasis, and cell viability independent of ANT1's nucleotide transport activity. The mutations act synergistically, as double mutant Aac2/ANT1 causes severe clogging primarily at the translocase of the outer membrane (TOM) complex. This confers extreme toxicity in yeast. In mice, expression of a super-clogger ANT1 variant led to neurodegeneration and an age-dependent dominant myopathy that phenocopy ANT1-induced human disease, suggesting clogging as a mechanism of disease. More broadly, this work implies the existence of uncharacterized amino acid requirements for mitochondrial carrier proteins to avoid clogging and subsequent disease.