bims-cytox1 2017-08-20 papers

Issue of 2017‒08‒20
three papers selected by
Gavin McStay
New York Institute of Technology

Cell. 2017 Aug 10. pii: S0092-8674(17)30819-X. [Epub ahead of print]170(4): 693-700.e7

Cryo-EM Structure of the TOM Core Complex from Neurospora crassa.

Thomas Bausewein, Deryck J Mills, Julian D Langer, Beate Nitschke, Stephan Nussberger, Werner Kühlbrandt.

The TOM complex is the main entry gate for protein precursors from the cytosol into mitochondria. We have determined the structure of the TOM core complex by cryoelectron microscopy (cryo-EM). The complex is a 148 kDa symmetrical dimer of ten membrane protein subunits that create a shallow funnel on the cytoplasmic membrane surface. In the core of the dimer, the β-barrels of the Tom40 pore form two identical preprotein conduits. Each Tom40 pore is surrounded by the transmembrane segments of the α-helical subunits Tom5, Tom6, and Tom7. Tom22, the central preprotein receptor, connects the two Tom40 pores at the dimer interface. Our structure offers detailed insights into the molecular architecture of the mitochondrial preprotein import machinery.

Keywords: TOM complex; cryo-EM; mitochondria; protein import

DOI: https://doi.org/10.1016/j.cell.2017.07.012

Mitochondrion. 2017 Aug 09. pii: S1567-7249(17)30149-6. [Epub ahead of print]

A mitochondrial proteomics view of complex I deficiency in Candida albicans.

Xiaodong She, Pengyi Zhang, Ying Gao, Lulu Zhang, Qiong Wang, Hui Chen, Richard Calderone, Weida Liu, Dongmei Li.

Proteomic analyses were carried out on isolated mitochondrial samples of C. albicans from gene-deleted mutants (nuo1Δ, nuo2Δ and goa1Δ) as well as the parental strain in order to better understand the contribution of these three fungal-specific mitochondrial ETC complex I (CI) subunits to cellular activities. Herein, we identify 2333 putative proteins from four strains, in which a total of 663 proteins (28.5%) are putatively located in mitochondria. Comparison of protein abundances between mutants and the parental strain reveal 146 differentially-expressed proteins, of which 78 are decreased and 68 are increased in at least one mutant. The common changes across the three mutants include the down-regulation of nuclear-encoded CI subunit proteins as well as phospholipid, ergosterol and cell wall mannan synthesis, and up-regulated proteins in CIV and the alternative oxidase (AOX2). As for gene-specific functions, we find that NUO1 participates in nucleotide synthesis and ribosomal biogenesis; NUO2 is involved in vesicle trafficking; and GOA1 appears to regulate membrane transporter proteins, ROS removal, and substrates trafficking between peroxisomes and mitochondria. The proteomic view of general as well as mutant-specific proteins further extends our understanding of the functional roles of non-mammalian CI-specific subunit proteins in cell processes. Particularly intriguing is the confirmation of a regulatory role for GOA1 on ETC function, a protein found almost exclusively in Candida species.SIGNIFICANCE: Fungal mitochondria are critical for fungal pathogenesis. The absence of any of the three fungal specific CI subunits in mitochondria causes an avirulence phenotype of C. albicans in a murine model of invasive disease. As model yeast (Saccharomyces cerevisiae) lacks a CI and is rarely a pathogen of humans, C. albicans is a better choice for establishing a link between mitochondrial CI and pathogenesis. Apart from the general effects of CI mutants on respiration, previous phenotyping of these mutants were quite similar to each other or to CI conservative subunit. By comparison to transcriptional data, the proteomic data obtained in this study indicate that biosynthetic events in each mutant such as cell wall and cell membrane phospholipids and ergosterol are generally decreased in both transcriptomal and translational levels. However, in the case of mitochondrial function, glycolysis/gluconeogenesis, and ROS scavengers, often gene changes are opposite that of proteomic data in mutants. We hypothesize that the loss of energy production in mutants is compensated by increases in protein levels of glycolysis, gluconeogenesis, and anti-ROS scavengers that at least extend mutant survival.

Keywords: Candida albicans; Fungal mitochondrial function; Liquid chromatography; Mitochondrial complex I; Oribtrap fusion MS; Proteomics

DOI: https://doi.org/10.1016/j.mito.2017.08.003

Can J Physiol Pharmacol. 2017 Aug 11.

Mechanism of TFAM Mediated Cardiomyocyte Protection.

George H Kunkel, Pankaj Chaturvedi, Nicholas Theilen, Rohit Nair, Suresh C Tyagi.

Although mitochondrial transcription factor A (TFAM) is a protective component of mitochondrial DNA and a regulator of calcium and reactive oxygen species (ROS) production, the mechanism remains unclear. In heart failure (HF), TFAM is significantly decreased and cardiomyocyte instability ensues. TFAM inhibits Nuclear Factor of Activated T cells (NFAT), which reduces ROS production; additionally, TFAM transcriptionally activates SERCA2a to decrease free calcium. Therefore, decreasing TFAM vastly increases protease expression and hypertrophic factors, leading to cardiomyocyte functional decline. To examine this hypothesis, treatments of 1.0 micrograms of a TFAM vector and 1.0 micrograms of a CRISPR-Cas9 TFAM plasmid were administered to HL-1 cardiomyocytes via lipofectamine transfection. Western blotting and confocal microscopy analysis show that CRISPR-Cas9 knockdown of TFAM significantly increased proteases Calpain1, MMP9 and regulators Serca2a, and NFAT4 protein expression. CRISPR knockdown of TFAM in HL-1 cardiomyocytes upregulates degratory factors, leading to cardiomyocyte instability. Hydrogen peroxide oxidative stress decreased TFAM expression and increased Calpain1, MMP9, and NFAT4 protein expression. TFAM overexpression normalizes pathological hypertrophic factor NFAT4 in the presence of oxidative stress.

DOI: https://doi.org/10.1139/cjpp-2016-0718