Evidence for Non-Essential Salt Bridges in the M-Gates of Mitochondrial Carrier Proteins

Mitochondrial carriers, which transport metabolites, nucleotides, and cofactors across the mitochondrial inner membrane, have six transmembrane α-helices enclosing a translocation pore with a central substrate binding site whose access is controlled by a cytoplasmic and a matrix gate (M-gate). The salt bridges formed by the three PX[DE]XX[RK] motifs located on the odd-numbered transmembrane α-helices greatly contribute to closing the M-gate. We have measured the transport rates of cysteine mutants of the charged residue positions in the PX[DE]XX[RK] motifs of the bovine oxoglutarate carrier, the yeast GTP/GDP carrier, and the yeast NAD+ transporter, which all lack one of these charged residues. Most single substitutions, including those of the non-charged and unpaired charged residues, completely inactivated transport. Double mutations of charged pairs showed that all three carriers contain salt bridges non-essential for activity. Two double substitutions of these non-essential charge pairs exhibited higher transport rates than their corre-sponding single mutants, whereas swapping the charged residues in these positions did not increase activity. The results demonstrate that some of the residues in the charged residue positions of the PX[DE]XX[KR] motifs are important for reasons other than forming salt bridges, probably for playing specific roles related to the substrate interaction-mediated conformational changes leading to the M-gate opening/closing

The Human SLC25A33 and SLC25A36 Genes of Solute Carrier Family 25 Encode Two Mitochondrial Pyrimidine Nucleotide Transporters

The human genome encodes 53 members of the solute carrier family 25 (SLC25), also called the mitochondrial carrier family, many of which have been shown to transport inorganic anions, amino acids, carboxylates, nucleotides, and coenzymes across the inner mitochondrial membrane, thereby connecting cytosolic and matrix functions. Here two members of this family, SLC25A33 and SLC25A36, have been thoroughly characterized biochemically. These proteins were overexpressed in bacteria and reconstituted in phospholipid vesicles. Their transport properties and kinetic parameters demonstrate that SLC25A33 transports uracil, thymine, and cytosine (deoxy)nucleoside di- and triphosphates by an antiport mechanism and SLC25A36 cytosine and uracil (deoxy)nucleoside mono-, di-, and triphosphates by uniport and antiport. Both carriers also transported guanine but not adenine (deoxy)nucleotides. Transport catalyzed by both carriers was saturable and inhibited by mercurial compounds and other inhibitors of mitochondrial carriers to various degrees. In confirmation of their identity (i) SLC25A33 and SLC25A36 were found to be targeted to mitochondria and (ii) the phenotypes of Saccharomyces cerevisiae cells lacking RIM2, the gene encoding the well characterized yeast mitochondrial pyrimidine nucleotide carrier, were overcome by expressing SLC25A33 or SLC25A36 in these cells. The main physiological role of SLC25A33 and SLC25A36 is to import/export pyrimidine nucleotides into and from mitochondria, i.e. to accomplish transport steps essential for mitochondrial DNA and RNA synthesis and breakdown

Favourable outcome of coronavirus disease 2019 in a patient with anaplastic lymphoma kinase-positive non-small-cell lung cancer receiving alectinib

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New Insights into the Evolution and Gene Structure of the Mitochondrial Carrier Family Unveiled by Analyzing the Frequent and Conserved Intron Positions

Mitochondrial carriers (MCs) belong to a eukaryotic protein family of transporters that in higher organisms is called the solute carrier family 25 (SLC25). All MCs have characteristic triplicated sequence repeats forming a 3-fold symmetrical structure of a six-transmembrane α-helix bundle with a centrally located substrate-binding site. Biochemical characterization has shown that MCs altogether transport a wide variety of substrates but can be divided into subfamilies, each transporting a few specific substrates. We have investigated the intron positions in the human MC genes and their orthologs of highly diversified organisms. The results demonstrate that several intron positions are present in numerous MC sequences at the same specific points, of which some are 3-fold symmetry related. Many of these frequent intron positions are also conserved in subfamilies or in groups of subfamilies transporting similar substrates. The analyses of the frequent and conserved intron positions in MCs suggest phylogenetic relationships not only between close but also distant homologs as well as a possible involvement of the intron positions in the evolution of the substrate specificity diversification of the MC family members

Superconducting Superstructure for the TESLA Collider

We discuss the new layout of a cavity chain (superstructure) allowing, we hope, significant cost reduction of the RF system of both linacs of the TESLA linear collider. The proposed scheme increases the fill factor and thus makes an effective gradient of an accelerator higher. We present mainly computations we have performed up to now and which encouraged us to order the copper model of the scheme, still keeping in mind that experiments with a beam will be necessary to prove if the proposed solution can be used for the acceleration.Comment: 11 page

TRANSCRIPTION OF THE MITOCHONDRIAL CITRATE CARRIER GENE: ROLE OF SREBP-1, UPREGULATION BY INSULIN AND DOWNREGULATION BY PUFA

In this study we investigated the transcriptional role of the sterol regulatory element (SRE) present in the promoter of the mitochon- drial citrate carrier (CIC). We show that wild-type (but not mutated) CIC SRE cloned in front of the luciferase promoter confers tran- scriptional activation of the gene reporter. We also demonstrate that insulin activates, and polyunsaturated fatty acids (PUFA) inhibit, the gene reporter activity driven by the CIC promoter containing wild-type (but not mutated) SRE. Finally, both insulin treatment and overexpression of SRE binding protein (SREBP-1) increase the CIC transcript and protein levels, whereas PUFA have an opposite effect. These results show that SRE/SREBP-1 play a role in the transcriptional regulation of CIC by insulin and PUFA

A key role of the mitochondrial citrate carrier (SLC25A1) in TNFα- and IFNγ-triggered inflammation

The chronic induction of inflammation underlies multiple pathological conditions, including metabolic, autoimmune disorders and cancer. The mitochondrial citrate carrier (CIC), encoded by the SLC25A1 gene, promotes the export of citrate from the mitochondria to the cytoplasm, a process that profoundly influences energy balance in the cells. We have previously shown that SLC25A1 is a target gene for lipopolysaccharide signaling and promotes the production of inflammatory mediators. We now demonstrate that SLC25A1 is induced at the transcriptional level by two key pro-inflammatory cytokines, tumor necrosis factor-α (TNFα) and interferon-γ (IFNγ), and such induction involves the activity of the nuclear factor kappa B and STAT1 transcription factors. By studying the down-stream events following SLC25A1 activation during signals that mimic inflammation, we demonstrate that CIC is required for regulating the levels of nitric oxide and of prostaglandins by TNFα or IFNγ. Importantly, we show that the citrate exported from mitochondria via CIC and its downstream metabolic intermediate, acetyl-coenzyme A, are necessary for TNFα or IFNγ to induce nitric oxide and prostaglandin production. These findings provide the first line of evidence that the citrate export pathway, via CIC, is central for cytokine-induced inflammatory signals and shed new light on the relationship between energy metabolism and inflammation

Malignant hypertension and hyperreninemia: Primary or secondary hypertension? A case report

Malignant hypertension is a rare condition characterized by severe hypertension and multi-organ ischemic damage. Marked activation of the renin-angiotensin system is observed in many patients, but its persistence over time is not known. We report a case of a 42-year-old woman who presented with severe hypertension and multi-organ damage. Initial evaluation showed an elevated value of direct renin concentration with normal plasma aldosterone concentration and a nodular lesion in the left adrenal gland. The differential diagnosis between the primary and secondary form of hypertension had to be questioned. Consequently, the patient was followed up for 20 months. Repeated checks showed a significant increase in renin levels with a normal aldosterone concentration and regression of organ damage. After 20 months, renin values returned within normal range. Hyperreninemia persisting over a long period of time has not been fully explained. Long-term follow-up allowed us to attribute malignant hypertension to de novo essential hypertension