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MitoNews
Mitochondrial Research Bulletin
Published by:
MitoSciences
Advancing Vital Discoveries in Mitochondrial Research
http://www.mitosciences.com
Edited & Written by:
Dr. Roderick Capaldi
[email protected]
Volume 01, Issue 07 - July 18, 2005
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In This Issue...
ANNOUNCEMENT
MitoSciences Launches a New Online Discussion Forum
RECENT RESEARCH
1. Mitochondrial type 1 nitric oxide synthase and cytochrome c
oxidase interact directly
2. Grim-19 mutations as a cause of Hurthie cell (thyroid) tumors
3. Stunted drosophila are missing the epsilon subunit of the
ATP synthase and do not orient the spindle properly in
development.
4. Time course of cytochrome c tyrosine nitration by
peroxynitirite: a biomarker for oxidative stress?
5. Proteomic analysis of mutant tau transgenic mice highlights
the mitochondrial dysfunction caused.
6. Rotation of the epsilon subunit in membrane-bound F1F0
has been followed by FRET
7. Aconitase, a Krebs cycle enzyme, is part of the mitochondrial
nucleoid involved in mtDNA maintainance.
8. Succinyl-Co-A synthetase: another nucleoid protein?
9. A link between cholera and mitochondria: modulation of
complex I levels.
10. Helicobacter pylori pathogenesis through mitochondrial
targeting.
11. Do mtDNA mutations increase oxidative stress:
the LHON answer is yes.
12. Cytochrome c in serum, a biomarker for fulminant hepatitis?
13. Proteomics shows post-translational modification of
mitochondrial proteins in chronic diabetes.
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ANNOUNCEMENT
....................................................................................................
MitoSciences has started an online discussion forum for posting
questions and providing responses related to mitochondrial
structure, functioning and pathology as well as reports and
questions and answers related to our products.
To access this discussion forum please go to:
http://www.mitosciences.com/forums
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RECENT RESEARCH
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1. Mitochondrial type 1 nitric oxide synthase and cytochrome c
oxidase interact directly
Nitric oxide NO acts physiologically in mitochondria as a regulator
of OXPHOS, through a reversible inhibition of cytochrome c
oxidase (COX) in competition with oxygen. A constitutive neuronal
mitochondrial nitric oxide synthase(NOS) has been described,
and in the study referenced below, the authors suggest that this
NOS could generate NO close to its physiological target and
thereby reduce pathophysiological effects, such as reaction
with H2O2 to form the highly damaging peroxynitrite. It is shown
that NOS and COX interact directly using electron miscroscopic
immunolocalization, co immunoprecipitation, and affinity
chromatography. Further, the authors show that the interaction
of COX with NOS involves subunit Va, which contains a
concensus sequence for binding of the PDZ domain of NOS.
PERSICHINI.T, MAZZONE.V,POLTICELLI.F, MORENO.S,
VENTURINI.G, CLEMENTI.E & COLASANTI. M.
Neurosci Lett. 384. 254-9 (2005)
2. Grim-19 mutations as a cause of Hurthie cell (thyroid) tumors
Hurthie cell tumors of the thyroid are characterized by an
excessive number of mitochondria. In the study below a gene
predisposing to the cancer mapping to chromosome 19 has
been identified as that for Grim19, a protein with dual function;
it is a subunit of complex I and is involved in cell death. Of 20
patients with sporadic Hurthie cell carcinoma, 3 had mutations
in Grim19 while none of the controls had mutations in this gene,
suggesting a link of the protein to tumor formation.
MAXIMO.V, BOTELHO.T, CAPELA.J, SOARES.P, LIMA.J,
TAVEIRA.A, AMARO.T, BARBOSA.P, PRETO.A, HARACH.HR,
WILLIAMS.D & SOBRINHO-SIMOES.M.
Brit. J. Cancer. 92. 1892-8 (2005)
3. Stunted drosophila are missing the epsilon subunit of the
ATP synthase and do not orient the spindle properly in
development.
The gene for the epsilon subunit of the ATP synthase, found
in screening flies for growth deficiencies, is called sun or
stunted. Loss of expression of this gene leads to a dramatic
delay in growth rate of first instar larvae, and ultimately to
death. In the study below it was shown that embryos lacking
maternally supplied sun have sixfold lower ATP synthesis
activity. Nuclei still migrate normally to the cortex but then
several abnormalities in development followed, the most
striking of which was that nuclei and spindles form lines
and clusters instead of adopting a regular spacing. This is
reflected in a failure to properly align nonsister centrosomes
during the telophase to interphase transition. The authors
argue that reduced ATP synthase activity selectively affects
molecular motors. An important relevance of this is that sun
is the ligand for the Methuselah receptor that regulates aging.
KIDD.T, ABU-SHUMAYS.R, KATZEN.A, SISSON.JC,
JIMINEZ.G, PINCHIN.S, SULLIVAN.W & ISH-HOROWICZ.D.
GENETICS 170. 679-708 (2005)
4. Time course of cytochrome c tyrosine nitration by
peroxynitirite: a biomarker for oxidative stress?
Oxidative damage from oxidative and nitrative radicals,
including peroxynitrite, is thought to be causative of several
late onset disorders including Parkinsons disease, non-insulin
dependent diabetes and even the aging process itself. As a
result there is considerable interest in defining biomarkers for
this oxidative damage. In the paper referenced below the
authors have analyzed peroxynitrite reaction with cytochrome c.
This small protein acts both in electron transfer and in
apoptosis. The protein has 4 Tyr residues that are highly
conserved. At low concentrations of reagent, peroxynitrite was
found to react mainly with Tyr 97 and 74, the two Tyr residues
most accessible to solvent. At higher doses, peroxynitrite also
modified Tyr 48 and 67. Modification of Tyr 97, 74 and 67
inhibited the electron transfer function of cytochrome c at the
same time as increasing the peroxidase activity of the protein.
BATTYHANY.C, SOUZA.JM, DURAN.R, CASSINA.A,
CERVENANSKY.C & RADI.R.
Biochemistry 44. 8038-46 (2005)
5. Proteomic analysis of mutant tau transgenic mice highlights
the mitochondrial dysfunction caused.
In the study below the altered protein levels caused by
overexpressing a mutant tau protein (P301L) in mice has been
analyzed by proteomics. These mutant tau protein-mice
develop classical neurofibrillary tangles. There are altered
levels of several mitochondrial proteins in these mice, including
down regulation of both the ATP synthase and complex I
subunits. These modifications were associated with higher
levels of reactive oxygen species, even though there was
increased expression of antioxidant enzymes. The lowered
levels of ATP synthase was also seen in the brains of patients
showing the form of parkinsonism linked to chromosome 17
(P301L FTDP-17 brains). Interestingly, the P301L mutation
appears to increase vulnerability to amyloid beta protein.
DAVID.DC, HAUPTMANN.S, SCHERPING.I, SCHUESSEL.K,
KEIL.U, RIZZU.P, RAVID.R, DROSE.S, BRANDT.U, MULLER.WE,
EXKERT.A & GOTZ.J.
J.Biol. Chem. 280. 23802-14 (2005)
6. Rotation of the epsilon subunit in membrane-bound F1F0
has been followed by FRET
Recent studies have shown that the epsilon subunit of the
bacterial and chloroplast F1F0 ATP synthase is a part of the
central stalk that acts as the rotor. This subunit changes
conformation to allow it to act as a rachet directing forward
(ATP synthesis) and backwards (ATP hydrolysis) reactions
depending on nucleotide conditions. In the study referenced
below, the authors have monitored movements of the epsilon
subunit relative to the b subunit (which is part of the stator) by
single molecule fluorescence energy transfer measurement
(FRET). The study was done using intact F1F0 incorporated
into lipid vesicles. Three distinct distances were found,
consistent with rotation through 3 sites each related to one of
the 3 catalytic sites per F1F0 molecule. It was shown that the
rotations occur in opposite directions in synthesis versus
hydrolysis mode. The 3 distances between epsilon and the
b subunits were different in so-called active and inactive
forms of the enzyme complex.
ZIMMERMANN.B, DIEZ.M, ZARRABI.N, GRABER.P &
BORSCH.M.
EMBO.J. 24. 2053-63 (2005)
7. Aconitase, a Krebs cycle enzyme, is part of the mitochondrial
nucleoid involved in mtDNA maintainance.
The work of Butow and colleagues over the last few years has
greatly clarified the previously mainly theoretical notion that
mtDNA is wrapped up with proteins in vivo. These workers
using yeast genetics and elegant biochemistry have identified
22 different proteins associated with mtDNA in so-called
nucleoids. One of these is the Krebs cycle enzyme aconitase.
In the study below it is shown that aconitase is essential for
maintainance of mtDNA independent of its catalytic function,
arguing that the enzyme may integrate metabolic signals to
mtDNA copy number and stability.
CHEN.XJ, WANG.X, KAUFMAN.BA & BUTOW. RA.
Science 307.714-7 (2005)
8. Succinyl-Co-A synthetase: another nucleoid protein?
In the paper below evidence is presented that a deleterious
mutation in succinyl Co-A synthetase affecting the activity of
this enzyme is responsible for encephalopathy with mtDNA
depletion. The authors propose that the disrupted mitochondrial
maintainance results from altered interaction of succinyl-CoA
synthetase with the mitochondrial nucleotide diphosphate kinase
in the nucleoids.
ELPELEG.O, MILLER.C, HERSHKOVITZ.E,
BITNER-GLINDZICZ.M, BONDI-RUBENSTEIN.G, RAHMAN.S,
PAGNAMENTA.A, ESHHAR.S & SAADA.A.
Am. J. Hum. Genet 76. 1081-6 (2005)
9. A link between cholera and mitochondria: modulation of
complex I levels.
In the study referenced below the authors study the effects of
infection with the cholera causing bacterium Vibrio cholerae
using cultured intestinal cells. ND5 a subunit of complex I was
found to be up-regulated following exposure to V. cholerae.
This up-regulation was not observed with heat treated bacterium
or E.coli strains. Infection with an a-flagellate (non-mobile) strain
of V. cholerae showed a 59 fold down regulation of ND5 while
hyper-adherent but low motility strains showed a remarkable
200-fold up-regulation. No up-regulation of total mitochondrial
copy number was observed but a 3 fold increase in Complex I
activity was found.
SARKAR.M, DAS.S, BANDYOPADHAYA.A, RAY.K &
CHAUDHURI.K.
FEBS Lett. 579. 3449-60 (2005).
10. Helicobacter pylori pathogenesis through mitochondrial
targeting.
In the review below evidence that the gastric pathogen H.
pylori acts on mitochondria is presented. This involves
mitochondrial localization of the toxin VacA in epithelial cells.
At the mitochondrion the toxin forms a channel, permeabilizing
the outer membrane, releasing pro-apoptotic proteins and
thereby causing cell death.
BLANK.S.R.
Trends Microbiol 13. 64-71 (2005).
11. Do mtDNA mutations increase oxidative stress:
the LHON answer is yes.
A long-standing question is how mutations in mtDNA, such as
those that cause Lebers hereditary optic neuropathy, cause the
observed pathophysiology. One suggestion is that besides
reducing OXPHOS enzyme levels in many cases, they increase
oxidative stress with consequences for cell signaling as well as
many metabolic processes. In the study below, cybrids were
formed using osteosarcomma cells as host to provide nuclear
genes and fibroblasts carrying homoplasmic mutations
11778/ND4, 3460/ND1 and 14484/ND6 to provide mtDNA.
Activities of various enzymes involved in detoxification of
oxidative stress including glutathione peroxidase, glutathione
reductase, superoxide dismutases and catalase, along with
GSH and GSSG, were measured. When cultured in glucose,
and living mainly by glycolysis, cells that had reduced
anti-oxidant enzymes as part of the phenotype had normal
levels of GSH and GSSG. However, when forced to live by
OXPHOS by culturing in galactose, GSSG concentrations were
found to increase while the levels of GR and Mn superoxide
dismutase further decreased in all LHON cybrids.
FLOREANI.M, NAPOLI.E, MARTINUZZI.A, PANTANO.G,
DE RIVA.V, TREVISAN.R, BISETTO.E, VALENTI.L, CRELLI.V
& DABBENI-SALA.F.
FEBS Lett. 272. 1124-35 (2005).
12. Cytochrome c in serum, a biomarker for fulminant hepatitis?
As evidence of the involvement of mitochondria in many human
diseases grows, the search for biomarkers among mitochondrial
proteins that distinguish these diseases intensifies. In the study
below it is shown that serum cytochrome c levels are an accurate
marker of the severity of hepatic coma. The obvious mechanism
is that the small protein is released as cells die from apoptotic or
necrotic death due to viral infection.
SAKAIDA.I, KIMURA.T, YAMASAKI.T, FUKUMOTO.Y,
WATANABE.K, AOYAMA.M & OKITA.K.
J. Gastroenterol 40. 179-85 (2005).
13. Proteomics shows post-translational modification of
mitochondrial proteins in chronic diabetes.
In the article below the authors examine the structural
alterations of proteins caused by chronic hyperglycemia.
Methylglyoxal-induced hydroimidazolones are the predominant
modifications found. Both proteomic analysis and functional
studies were performed in renal cortical mitochondria isolated
from rats with 2, 6, and 12 mo of streptozotocin-induced
diabetes. MGO-modification occurred in OXPHOS proteins and
in particular in two subunits of complex III, with consequent
lowered complex III activity that was significantly correlated
with the quantity of MGO-derived hydroimidazolone present.
The implication is that posttranslational modifications of
mitochondrial proteins by MGO causes pathogenic events
leading to mitochondria-induced oxidative stress in the kidney
in chronic diabetes.
ROSCA.MG, MUSTATA.TG, KINTER.MT, OZDEMIR.AM,
KERN.TS, SZWEDA.LI, BROWNLEE.M, MONNIER. VM &
WEISS.MF
Am. J. Physiol. Renal. Physiol. 289 F420-30 (2005)
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