The TOB/SAM complex: an essential function in mitochondria biogenesis

Białka tworzące strukturę beczułki b występują w błonie zewnętrznej bakterii Gramujemnych oraz w błonie zewnętrznej organelli pochodzenia endosymbiotycznego, tj. mitochondriów i chloroplastów, gdzie mogą pełnić różne funkcje. Mitochondrialne białka o strukturze beczułki b biorą udział w imporcie białka, transporcie metabolitów oraz w regulacji morfologii i dystrybucji mitochondriów. Białka te uznaje siê takze za istotny element ewolucji mitochondriów. Mechanizm wbudowywania białek tworzących strukturę beczułki b w błone zewnętrzną mitochondriów i bakterii Gram-ujemnych został niedawno opisany. Co więcej, wykazano, iż uległ on utrwaleniu w toku ewolucji. W przypadku mitochondriów w procesie tym uczestniczy kompleks TOB/SAM (topogeneza białek zewnętrznej błony mitochondrialnej tworzących strukturę beczułki b/maszyneria sortowania i składania białek), tworzony przez trzy podstawowe białka: Tob55 (Sam50), Tob38 (Sam35) and Mas 37 (Sam37). Wyniki analizy filogenetycznej wskazują, iż białko Tob55 pochodzi od bakteryjnego białka Omp85, podczas gdy inne mitochondrialne białka o strukturze beczułki b nie mają homologów wśród białek bakteryjnych.b-barrel proteins are present in the outer membrane of Gram-negative bacteria and of organelles of endosymbiotic origin, i.e. mitochondria and chloroplasts where they perform a variety of functions. Mitochondrial b-barrel proteins are important for protein import, metabolite transport and the organelle morphology and distribution. They also seem to play a crucial role in mitochondria evolution. Quite recently a specific pathway for the insertion of b-barrel proteins was identified in both mitochondria and Gram-negative bacteria and was proved to be conserved during evolution. In mitochondria the pathway is formed by the TOB/SAM complex (topogenesis of the mitochondrial outer membrane b-barrel proteins/ sorting and assembly machinery) composed of three main proteins, namely Tob55 (Sam50), Tob38 (Sam35) and Mas 37 (Sam37). Phylogenetic analysis provides a strong case for the evolution of Tob55 from the bacterial homologue Omp85 while other mitochondrial b-barrel proteins do not display amino acid homology with bacterial b-barrel proteins

Communication between mitochondria and nucleus: Putative role for VDAC in reduction/oxidation mechanism

AbstractVoltage dependent anion channel (VDAC) was identified in 1976 and since that time has been extensively studied. It is well known that VDAC transports metabolites across the outer mitochondrial membrane. The simple transport function is indispensable for proper mitochondria functions and, consequently for cell activity, and makes VDAC crucial for a range of cellular processes including ATP rationing, Ca2+ homeostasis and apoptosis execution. Here, we review recent data obtained for Saccharomyces cerevisiae cells used as a model system concerning the putative role of VDAC in communication between mitochondria and the nucleus. The S. cerevisiae VDAC isoform known as VDAC1 (termed here YVDAC) mediates the cytosol reduction/oxidation (redox) state that contributes to regulation of expression and activity of cellular proteins including proteins that participate in protein import into mitochondria and antioxidant enzymes. Simultaneously, copper-and-zinc-containing superoxide dismutase (CuZnSOD) plays an important role in controlling YVDAC activity and expression levels. Thus, it is proposed that VDAC constitutes an important component of a regulatory mechanism based on the cytosol redox state

Mitochondrial Processes during Early Development of Dictyostelium discoideum: From Bioenergetic to Proteomic Studies

The slime mold Dictyostelium discoideum’s life cycle includes different unicellular and multicellular stages that provide a convenient model for research concerning intracellular and intercellular mechanisms influencing mitochondria’s structure and function. We aim to determine the differences between the mitochondria isolated from the slime mold regarding its early developmental stages induced by starvation, namely the unicellular (U), aggregation (A) and streams (S) stages, at the bioenergetic and proteome levels. We measured the oxygen consumption of intact cells using the Clarke electrode and observed a distinct decrease in mitochondrial coupling capacity for stage S cells and a decrease in mitochondrial coupling efficiency for stage A and S cells. We also found changes in spare respiratory capacity. We performed a wide comparative proteomic study. During the transition from the unicellular stage to the multicellular stage, important proteomic differences occurred in stages A and S relating to the proteins of the main mitochondrial functional groups, showing characteristic tendencies that could be associated with their ongoing adaptation to starvation following cell reprogramming during the switch to gluconeogenesis. We suggest that the main mitochondrial processes are downregulated during the early developmental stages, although this needs to be verified by extending analogous studies to the next slime mold life cycle stages

Potential oxidative stress related targets of mitochondria-focused therapy of PTSD

Post-traumatic stress disorder (PTSD) remains a highly prevalent, under-diagnosed, and under-treated psychiatric disorder that often deteriorates over time, and is highly comorbid with major depressive disorder, suicidality, and substance use disorder. Several biomarkers have been proposed but have yet to be implemented into clinical practice. Treatments, including selective serotonin reuptake inhibitors, are efficacious in only a small number of patients, which underscores the need to develop novel, efficient treatments. Mitochondrial dysfunction resulting from chronic oxidative stress has been linked with both altered neurotransmitter signaling and the inflammatory response. Hereinafter, we discuss mechanisms by which mitochondrial dysfunction may contribute to the development of PTSD symptoms, and how these may even increase PTSD susceptibility. We also highlight possible therapeutic targets to reduce oxidative stress to prevent or treat PTSD symptoms

Verification of Hypsibius exemplaris Gąsiorek et al., 2018 (Eutardigrada; Hypsibiidae) application in anhydrobiosis research

Anhydrobiosis is considered to be an adaptation of important applicative implications because it enables resistance to the lack of water. The phenomenon is still not well understood at molecular level. Thus, a good model invertebrate species for the research is required. The best known anhydrobiotic invertebrates are tardigrades (Tardigrada), considered to be toughest animals in the world. Hypsibius. exemplaris is one of the best studied tardigrade species, with its name “exemplaris” referring to the widespread use of the species as a laboratory model for various types of research. However, available data suggest that anhydrobiotic capability of the species may be overestimated. Therefore, we determined anhydrobiosis survival by Hys. exemplaris specimens using three different anhydrobiosis protocols. We also checked ultrastructure of storage cells within formed dormant structures (tuns) that has not been studied yet for Hys. exemplaris. These cells are known to support energetic requirements of anhydrobiosis. The obtained results indicate that Hys. exemplaris appears not to be a good model species for anhydrobiosis research. Introductio

Methadone induces necrotic-like cell death in SH-SY5Y cells by an impairment of mitochondrial ATP synthesis

Methadone is a widely used therapeutic opioid in narcotic addiction and neuropathic pain syndromes. Oncologists regularly use methadone as a long-lasting analgesic. Recently it has also been proposed as a promising agent in leukemia therapy, especially when conventional therapies are not effective. Nevertheless, numerous reports indicate a negative impact on human cognition with chronic exposure to opiates. Thus, clarification of methadone toxicity is required. In SH-SY5Y cells we found that high concentrations of methadone were required to induce cell death. Methadone-induced cell death seems to be related to necrotic processes rather than typical apoptosis. Cell cultures challenged with methadone presented alterations in mitochondrial outer membrane permeability. A mechanism that involves Bax translocation to the mitochondria was observed, accompanied with cytochrome c release. Furthermore, no participation of known protein regulators of apoptosis such as Bcl-XL and p53 was observed. Interestingly, methadone induced cell death took place by a caspases-independent pathway; perhaps due to its ability to induce a drastic depletion in cellular ATP levels. Therefore, we studied the effect of methadone on isolated rat liver mitochondria. We observed that methadone caused mitochondrial uncoupling, coinciding with the ionophoric properties of methadone, but did not cause swelling of the organelles. Overall, the effects observed for cells in the presence of supratherapeutic doses of methadone may result from a “bioenergetic crisis.” A decreased level of cellular energy may predispose cells to necrotic-like cell death

Phylogenetic Analysis of Mitochondrial Outer Membrane β-Barrel Channels

Transport of molecules across mitochondrial outer membrane is pivotal for a proper function of mitochondria. The transport pathways across the membrane are formed by ion channels that participate in metabolite exchange between mitochondria and cytoplasm (voltage-dependent anion-selective channel, VDAC) as well as in import of proteins encoded by nuclear genes (Tom40 and Sam50/Tob55). VDAC, Tom40, and Sam50/Tob55 are present in all eukaryotic organisms, encoded in the nuclear genome, and have β-barrel topology. We have compiled data sets of these protein sequences and studied their phylogenetic relationships with a special focus on the position of Amoebozoa. Additionally, we identified these protein-coding genes in Acanthamoeba castellanii and Dictyostelium discoideum to complement our data set and verify the phylogenetic position of these model organisms. Our analysis show that mitochondrial β-barrel channels from Archaeplastida (plants) and Opisthokonta (animals and fungi) experienced many duplication events that resulted in multiple paralogous isoforms and form well-defined monophyletic clades that match the current model of eukaryotic evolution. However, in representatives of Amoebozoa, Chromalveolata, and Excavata (former Protista), they do not form clearly distinguishable clades, although they locate basally to the plant and algae branches. In most cases, they do not posses paralogs and their sequences appear to have evolved quickly or degenerated. Consequently, the obtained phylogenies of mitochondrial outer membrane β-channels do not entirely reflect the recent eukaryotic classification system involving the six supergroups: Chromalveolata, Excavata, Archaeplastida, Rhizaria, Amoebozoa, and Opisthokonta