The TOM Complex of Amoebozoans: the Cases of the Amoeba Acanthamoeba castellanii and the Slime Mold Dictyostelium discoideum.

Protein import into mitochondria requires a wide variety of proteins, forming complexes in both mitochondrial membranes. The TOM complex (translocase of the outer membrane) is responsible for decoding of targeting signals, translocation of imported proteins across or into the outer membrane, and their subsequent sorting. Thus the TOM complex is regarded as the main gate into mitochondria for imported proteins.

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.

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

Voltage 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.

Cu,Zn-superoxide dismutase is necessary for proper function of VDAC in Saccharomyces cerevisiae cells.

Available data suggest that a copper-and zinc-containing dismutase (CuZnSOD) plays a significant role in protecting eukaryotic cells against oxidative modifications which may contribute to cell aging. Here we demonstrated that depletion of CuZnSOD in Saccharomyces cerevisiae cells (Deltasod1 cells) affected distinctly channel activity of VDAC (voltage dependent anion selective channel) and resulted in a moderate reduction in VDAC levels as well as in levels of protein crucial for VDAC import into mitochondria, namely Tob55/Sam50 and Tom40. The observed alterations may result in mitochondriopathy and subsequently in the shortening of the replicative life span observed for S.

Response of Acanthamoeba castellanii mitochondria to oxidative stress.

The purpose of this study was to examine the effects of oxidative stress caused by hydroperoxide (H(2)O(2)) in the presence of iron ions (Fe(2+)) on mitochondria of the amoeba Acanthamoeba castellanii. We used isolated mitochondria of A. castellanii and exposed them to four levels of H(2)O(2) concentration: 0.

Effects of VDAC isoforms on CuZn-superoxide dismutase activity in the intermembrane space of Saccharomyces cerevisiae mitochondria.

Copper and zinc containing superoxide dismutase (CuZnSOD) is located primarily in the cytosol but a small amount of the enzyme has also been identified in the intermembrane space of mitochondria (termed here IMS CuZnSOD). Using Saccharomyces cerevisiae mutants depleted of either isoform of VDAC (voltage-dependent anion-selective channel), we have shown that the activity of IMS CuZnSOD coincides with the presence of a given VDAC isoform and changes in a growth phase dependent way. Moreover, the IMS CuZnSOD activity correlates with the levels of O2*- release from mitochondria and the cytosol redox state.

[The VDAC channel as the mitochondria function regulator].

Regulation of mitochondria physiology, indispensable for proper cell activity, requires an efficient exchange of molecules between mitochondria and cytoplasm at the level of the mitochondrial outer membrane. The common pathway for the metabolite exchange between mitochondria and cytoplasm is the VDAC channel (voltage dependent anion channel), known also as mitochondrial porin. The channel was identified for the first time in 1976 and since that time has been extensively studied.

An inception report on the TOM complex of the Amoeba Acanthamoeba castellanii, a simple model protozoan in mitochondria studies.

It is suggested that in the course of the TOM complex evolution at least two lineages have appeared: the animal-fungal and green plant ones. The latter involves also the TOM complexes of algae and protozoans. The amoeba Acanthamoeba castellanii is a free-living non-photosynthetic soil protozoan, whose mitochondria share many bioenergetic properties with mitochondria of plants, animals and fungi.

Modulation of the voltage-dependent anion-selective channel by cytoplasmic proteins from wild type and the channel depleted cells of Saccharomyces cerevisiae.

It is well known that effective exchange of metabolites between mitochondria and the cytoplasm is essential for cell physiology. The key step of the exchange is transport across the mitochondrial outer membrane, which is supported by the voltage-dependent anion-selective channel (VDAC). Therefore, it is clear that the permeability of VDAC must be regulated to adjust its activity to the actual cell needs.

The key role of the energized state of Saccharomyces cerevisiae mitochondria in modulations of the outer membrane channels by the intermembrane space proteins.

Mitochondria of the yeast Saccharomyces cerevisiae constitute a perfect model to study the outer membrane channel modulation as besides the TOM complex channel they contain only a single isoform of the VDAC channel and it is possible to obtain viable mutants devoid of the channel. Here, we report that the fraction of the intermembrane space isolated from wild type and the VDAC channel-depleted yeast mitochondria, except of the well-known VDAC channel modulator activity, displays also the TOM complex channel modulating activity as measured in the reconstituted system and with intact mitochondria. The important factor influencing the action of both modulating activities is the energized state of mitochondria.