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Studies of enzymes in mitochondrial DNA precursor synthesis

regulatory mechanisms for human thymidine kinase 2 and deoxyguanosine kinase

Sun, Ren (2013). Studies of enzymes in mitochondrial DNA precursor synthesis. Diss. (sammanfattning/summary) Uppsala : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae, 1652-6880 ; 2013:64
ISBN 978-91-576-7866-9
eISBN 978-91-576-7867-6
[Doctoral thesis]

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As important enzymes in mitochondrial nucleotide salvage pathway, thymidine kinase 2 (TK2) and deoxyguanosine kinase (dGK) are expressed constitutively in almost all cells. These two enzymes catalyze the initial rate-limiting phosphorylation of pyrimidine and purine deoxynucleosides, respectively, providing DNA precursors for mitochondrial DNA (mtDNA) replication.

Inherited genetic defects in TK2 have been associated with infantile myopathic form of mtDNA depletion syndrome (MDS). In study I, two mutations, R225W and a novel T230A, in TK2 are identified as a new genetic cause of adult-onset autosomal recessive progressive external ophthalmoplegia (arPEO) and the kinetic and structural effects of the two mutations on enzyme function have been characterized.

Nucleoside analogs are widely used in anti-viral and anti-cancer chemotherapy, but they can cause severe side-effect such as mtDNA depletion. In study II, the potential mechanism underlying pyrimidine nucleoside analogs-associated mitochondrial toxicities was investigated, and showed that thymidine analogs had opposite effects on dThd and dCyd phosphorylation and thus can inhibit dThd salvage, leading to imbalanced dTTP and dCTP pools. It was found that the mechanism is most likely due to that TK2 normally exists in an inactive form with bound dTTP.

The redox regulation of TK2 and dGK was studied in study III and IV. The activity of both enzymes was sensitive to the cellular redox status. Under oxidative stress, both TK2 and dGK can be reversibly S-glutathionylated by GSSG. The modification of the conserved Cys189 in TK2 was responsible for a partial inactivation and selective degradation of TK2 in mitochondria, most likely via the AAA⁺ Lon protease. The oxidative effect of nucleoside analogs was also evaluated. Treatment with 3’-azido- 2’,3’-dideoxythymidine (AZT) and 2’,3’-dideoxyinosine (ddI) led to degradation of mitochondrial TK2 and dGK, whereas uridine and guanosine supplementations to AZT respective ddI treatments prevented both proteins from degradation.

Authors/Creators:Sun, Ren
Title:Studies of enzymes in mitochondrial DNA precursor synthesis
Subtitle:regulatory mechanisms for human thymidine kinase 2 and deoxyguanosine kinase
Series Name/Journal:Acta Universitatis Agriculturae Sueciae
Year of publishing :September 2013
Number of Pages:76
I.*Tyynismaa, H., *Sun, R., Ahola-Erkkila, S., Almusa, H., Poyhonen, R., Korpela, M., Honkaniemi, J., Isohanni, P., Paetau, A., Wang, L. & Suomalainen, A. (2012). Thymidine kinase 2 mutations in autosomal recessive progressive external ophthalmoplegia with multiple mitochondrial DNA deletions. Hum Mol Genet 21(1), 66-75.
II.Wang, L., Sun, R. & Eriksson, S. (2011). The kinetic effects on thymidine kinase 2 by enzyme-bound dTTP may explain the mitochondrial side effects of antiviral thymidine analogs. Antimicrob Agents Chemother 55(6), 2552-8.
III.Sun, R., Eriksson, S. & Wang, L. (2012). Oxidative stress induced Sglutathionylation and proteolytic degradation of mitochondrial thymidine kinase 2. J Biol Chem 287(29), 24304-12.
IV.Sun, R., Eriksson, S. & Wang, L. The role of S-glutathionylation in degradation of mitochondrial thymidine kinase 2 and deoxyguanosine kinase: potential implication for toxicities of nucleoside analogs. Manuscript.
UNSPECIFIED* Shared first authorship
Place of Publication:Uppsala
Publisher:Department of Anatomy, Physiology and Biochemistry, Swedish University of Agricultural Sciences
ISBN for printed version:978-91-576-7866-9
ISBN for electronic version:978-91-576-7867-6
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:X Agricola extesions > X30 Life sciences
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Biochemistry and Molecular Biology
Agrovoc terms:enzymes, thymidine, kinases, mitochondria, dna
Keywords:Thymidine kinase 2, Deoxyguanosine kinase, Mitochondrial DNA, Progressive external ophthalmoplegia, Nucleoside analogs, AZT (3’-azido-2’,3’- dideoxythymidine), ddI (2’,3’-dideoxyinosine), S-glutathionylation
Permanent URL:
ID Code:10780
Department:(VH) > Dept. of Anatomy, Physiology and Biochemistry
Deposited By: Mr Ren Sun
Deposited On:04 Sep 2013 12:30
Metadata Last Modified:13 Dec 2014 23:52

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