dNMP Kinase Activity in Mitochondria and Its Role in Mitochondrial Mutagenesis Brian M.
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Transcript dNMP Kinase Activity in Mitochondria and Its Role in Mitochondrial Mutagenesis Brian M.
dNMP Kinase Activity in
Mitochondria and Its Role in
Mitochondrial Mutagenesis
Brian M. Blair
Dr. Christopher K.
Mathews
Department of
Biochemistry and
Biophysics
Oregon State
University
HHMI Research 2007
http://www.nsf.gov/news/overviews/biology/assets/interact08.jpg
Why Is Research on mtDNA
Metabolism Important?
http://en.wikipedia.org/wiki/Intermembrane_space_of_mitochondria
http://www.ccc.columbia.edu/Mitochondrial_Diseases/mito/round.gif
Semiautonomous
mtDNA
has 10-100
eukaryotic
organelle
fold
higher mutation
rate
Responsible
for ATP
than nuclear
synthesis
DNA
Functionspassed
linked to:
Mutations
from
generation to
Apoptosis
generation
Aging process
Sensitivity
Less
effectiveto antiHIV repair
drugs
mtDNA
mechanism
Contain their own
genome:
mtDNA
mtDNA
mutations =
disease
Mitochondrial Disease
Researchers have now
discovered over 40
types of mitochondrial
disease
40,000-70,000
Americans affected
Many age-related
diseases involve
defects of
mitochondrion
Diseases
involving altered
mitochondrial
function:
Parkinson’s
Disease
Alzheimer’s
Disease
Type 2 Diabetes
Various Cancers
Neurodegenerative
Disorders
Cardiomyopathies
Deoxyribonucleoside Triphosphates
(dNTPs)
Four mtDNA
precursors:
dATP
dGTP
dCTP
dTTP
Deoxyadenosine
triphosphate
Deoxyguanosine
triphosphate
Deoxythymidine
triphosphate
Deoxycytidine
dNTP pool
asymmetries =
mtDNA mutagenesis
triphosphate
Metabolic Routes to
Intramitochondrial dNTPs
Pathways
involving
dNMPs
Formation by
salvage route
Are the
pathways
involving
dNMPs
significant in
forming the
dNTP pool
asymmetries?
Purpose
Design an assay to measure dNMP phosphorylation to
dNDP within the mitochondrion
Measure enzymatic activity of dNMP kinase
Brain, Liver, Heart, Skeletal Muscle, and Kidneys
3) Measure the dNMP kinase activity using dTMP,
dGMP, dCMP, and dAMP as substrates
Hypothesis #1
The dNMP kinase activity will vary within the different
mammalian tissue mitochondria.
Analysis of this activity will help explain the different
uptake pathways in dNMP metabolism and possible
reasons behind dNTP asymmetry.
dNMP Kinase
-P-P*
dNDP
dN
dNMP
ATP
A-P-P-P*
ADP
Method 1: TLC Assay
Develop assay using T4 infected E. coli
HB101/pBK5 recombinant
ATP-γ-P33 to trace activity of dNMP kinase
Rxn Mixture:
0.2 M Tris-HCl, pH 7.8; 0.02 M MgCl2; 0.02 M
ATP; 2.0 mM dTMP
Use 50 µL rxn mixture with substrate, 0.1 µCi ATPγ-P33, 10 µL rat mitochondrial extract, water to 100
µL
Run on TLC in 0.5 M LiCl and 5% Na2B4O7,
pH 7.0 aqueous solvent
Measure cpm of dNDP and calculate specific
activity of enzyme
Results of TLC Data
No substrate control consistently has more counts
than the with dTMP substrate
1) Test ATP-γ-P33 for contamination
2) Original problem still present
Assay Test
TLC Reaction w/ New P33
9000
7000
60 min
5000
4000
3000
15000
5000
1000
0
0
5
10
15
20
Length (cm)
Other attempts to fix:
Remove small molecules or preexisting substrates from extract
Run TLC in 10 different solvent
systems
25
30 min
dTDP CPM
10000
2000
-1000 0
0 sub
20000
CPM
6000
CPM
25000
No Enz/Sub
heat 2 min
P33
8000
0 min
1
2
3
4
Reactions
Results:
Still co-migration occurs
TLC assay cannot be used
Method 2: HPLC Assay
0.2 M Tris-HCl, pH 7.8; 0.02 M MgCl2; 0.02 M
ATP; 2.0 mM dTMP
Use 50 µL rxn mixture with substrate, 10 µL rat
mitochondrial extract, water to 100 µL
Dilute 20-fold and run in HPLC
Run standards to label nucleotides during rxn
Nucleotide Standards
ADP
ATP
dTDP
AMP
dTMP
dTTP
0’ Rxn
30’ Rxn
ATP
ATP
ADP
1? 2?
dTMP
ADP
60’ Rxn
Thy dTMP
1?
ATP
ATP
ADP
1?
Thy
ADP
Thy
2?
dTMP
2?
dTMP
0 dTMP Substrate
1?
ADP
2?
ATP
120’ Rxn
Results of Reactions
dTMP Concentrations vs. Reaction Times
Area Concentration
3000000
2500000
2000000
dTMP Concentrations
1500000
No Substrate (dTMP) Control
1000000
500000
0
0
50
100
150
Time (minutes)
Hypothesis #2
dTMP is getting broken down to thymidine
and Pi as part of the 5’-deoxynucleotidase
activity and regulation pathway
Thy
dTMP
Thy
0 ATP 0’
1mM Thymidine
Thy
0 ATP 60’
Explanation of dTMP Data
Removal of ATP
blocks formation of
dTMP from
thymidine
Result:
All dTMP gets
converted to
thymidine and Pi
Activity of 5’deoxynucleotidase
high in rat liver
mitochondria
Summary
Developed assay using thin layer chromatography to measure
enzymatic activity of dNMP kinase
Co-migration of unknown products at dTDP designated area
Used HPLC to visualize elution times and peak areas; I found
two unknown reaction products formed
Proved activity of 5’-deoxynucleotidase forming thymidine
from dTMP in absence of ATP; activity is high in rat liver
mitochondria
Future Research Goals
Continue to perfect the HPLC assay
Pursue the other reactions that are occurring
and find the reason behind this occurrence
Use mass spectrometer to determine molecular
weight of unknown products
Measure the dNMP kinase activity of the
four different deoxynucleotides within the
different tissue mitochondria
Acknowledgements
Howard Hughes Medical
Institute
Dr. Christopher K.
Mathews
Linda Benson
Dr. Kevin Ahern
Oregon State University
Funding:
Howard Hughes
Medical Institute