Mitochondrial dNTP supply for mtDNA maintenance — MNGIE and mtDNA depletion syndromes

Faithful replication of mitochondrial DNA (mtDNA), including in post-mitotic tissues, requires a balanced supply of the four deoxyribonucleoside triphosphates (dNTPs) inside mitochondria. Because mitochondria cannot rely on the cell-cycle-regulated cytosolic de novo machinery, they use a dedicated salvage pathway plus a p53-inducible de novo input, and depend on cytosolic enzymes that keep nucleoside pools balanced. The mitochondrial deoxyribonucleoside kinases phosphorylate imported deoxyribonucleosides to dNMPs: thymidine kinase 2 (TK2) handles the pyrimidines (thymidine, deoxycytidine, deoxyuridine) and deoxyguanosine kinase (DGUOK) the purines (deoxyguanosine, deoxyadenosine). The p53-inducible ribonucleotide reductase small subunit RRM2B (p53R2), with RRM1, provides de novo deoxyribonucleoside diphosphates (dNDPs) by reducing NDPs — the main dNTP source for quiescent cells and mtDNA. Cytosolic thymidine phosphorylase (TYMP) governs systemic thymidine/deoxyuridine levels; its loss floods the dNTP pool with thymidine-derived nucleotides and destabilises mtDNA. Together these enzymes maintain the mitochondrial dNTP balance; imbalance (excess or deficiency) causes mtDNA depletion/deletions. Inherited defects are the classic mtDNA-maintenance disorders: TYMP -> MNGIE; TK2 -> myopathic mtDNA depletion; DGUOK -> hepatocerebral mtDNA depletion; RRM2B -> encephalomyopathic mtDNA depletion and dominant progressive external ophthalmoplegia.

MODULE:mitochondrial_dntp_supplyDRAFTMetabolic Pathwaymodules/mitochondrial_dntp_supply.yaml
deoxyribonucleotide biosynthetic processGO:0009263
GO:0009263
deoxyribonucleotide biosynthetic process
The module groups the enzymes that supply/balance the mitochondrial dNTP pool (deoxyribonucleotide biosynthetic process, GO:0009263) for mtDNA replication.
GO:0006264
mitochondrial DNA replication
The physiological endpoint served is mitochondrial DNA replication (GO:0006264); dNTP imbalance from defects in these enzymes causes mtDNA depletion/instability.
file:human/TK2/TK2-ai-review.yaml
TK2 gene review (human)
The mitochondrial pyrimidine deoxyribonucleoside-salvage step (UniProtKB:O00142, GO:0004797) matches the completed human TK2 review.
file:human/DGUOK/DGUOK-ai-review.yaml
DGUOK gene review (human)
The mitochondrial purine deoxyribonucleoside-salvage step (UniProtKB:Q16854, GO:0004138) matches the completed human DGUOK review.
file:human/RRM2B/RRM2B-ai-review.yaml
RRM2B gene review (human)
The p53-inducible de novo dNDP-supply step (UniProtKB:Q7LG56, GO:0004748) matches the completed human RRM2B review.
file:human/TYMP/TYMP-ai-review.yaml
TYMP gene review (human)
The thymidine-pool-regulating step (UniProtKB:P19971, GO:0009032) matches the completed human TYMP review.
5Nodes
4Parts
0Variant Sets
0Variants
4Annotons
0Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

No MODULE:mitochondrial_dntp_supply deep-research report alongside the module YAML.

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Gene-review completeness (4/4 grounded genes reviewed)

4 complete review(s) · 0 with deep research · 0 missing review · 4 reviewed but lacking deep research

Gene Review Complete Deep research
DGUOK Q16854 ✓ ✓ ✗
RRM2B Q7LG56 ✓ ✓ ✗
TK2 O00142 ✓ ✓ ✗
TYMP P19971 ✓ ✓ ✗

Details

Context
mitochondrionGO:0005739
Mitochondrial dNTP supply (mtDNA maintenance)Metabolic Pathwaymitochondrial_dntp_supply
deoxyribonucleotide biosynthetic processGO:0009263
Context
mitochondrionGO:0005739

Mitochondrial dNTP-supply / mtDNA-maintenance system grounded to the human enzymes TK2 (UniProtKB:O00142, GO:0004797, EC 2.7.1.21), DGUOK (Q16854, GO:0004138, EC 2.7.1.113), RRM2B (Q7LG56, GO:0004748, EC 1.17.4.1) and TYMP (P19971, GO:0009032, EC 2.4.2.4). GO molecular-function terms were taken from the human GOA records; Reactome reaction ids and titles were verified against the local reactome cache. Each node uses a PANTHER family selector with the human enzyme as representative (TK2 and DGUOK are paralogs in the same deoxyribonucleoside-kinase family PTHR10513, with the cytosolic DCK/TK1 relatives; RRM2B is the p53-inducible paralog of the cell-cycle RRM2). This is a CONVERGENT-supply module rather than a linear pathway: TK2 (pyrimidine) and DGUOK (purine) salvage imported deoxyribonucleosides to dNMPs inside the matrix; RRM2B/RRM1 supply de novo dNDPs (cytosolic, imported); and TYMP keeps the thymidine/deoxyuridine pool balanced. The dNMPs/dNDPs are further phosphorylated (CMPK/NME kinases) to the dNTPs used by the mtDNA replisome (POLG). Their shared endpoint is a balanced mitochondrial dNTP pool for mtDNA replication (GO:0006264); genetic imbalance in any of them causes an mtDNA-maintenance disorder: TYMP -> MNGIE; TK2 -> myopathic mtDNA depletion (MTDPS2); DGUOK -> hepatocerebral mtDNA depletion (MTDPS3); RRM2B -> encephalomyopathic mtDNA depletion (MTDPS8) and autosomal-dominant progressive external ophthalmoplegia. RRM2B's dNTP supply and TYMP's angiogenic (PD-ECGF) moonlighting are captured in the respective gene reviews.

Part 1: mitochondrial pyrimidine deoxyribonucleoside salvage
thymidine / deoxycytidine / deoxyuridine + ATP to dTMP / dCMP / dUMPReactiontk2_step

Annotons

TK2: mitochondrial thymidine kinase 2
tk2_activity
Participant: Family: Deoxyribonucleoside kinase family (TK2/DGUOK/DCK)
Family:
Deoxyribonucleoside kinase family (TK2/DGUOK/DCK)PANTHER:PTHR10513
Representative Members: TK2 (human)UniProtKB:O00142

Function

thymidine kinase activityGO:0004797
Substrates: thymidine / deoxycytidine / deoxyuridine ATP
Products: dTMP / dCMP / dUMP ADP

Locations

mitochondrial matrixGO:0005759

Pyrimidine arm of the mitochondrial deoxyribonucleoside salvage pathway, phosphorylating thymidine/deoxycytidine/deoxyuridine to dNMPs for mtDNA. Deficiency = myopathic mtDNA depletion syndrome (MTDPS2).

Part 2: mitochondrial purine deoxyribonucleoside salvage
deoxyguanosine / deoxyadenosine + ATP to dGMP / dAMPReactiondguok_step

Annotons

DGUOK: mitochondrial deoxyguanosine kinase
dguok_activity
Participant: Family: Deoxyribonucleoside kinase family (TK2/DGUOK/DCK)
Family:
Deoxyribonucleoside kinase family (TK2/DGUOK/DCK)PANTHER:PTHR10513
Representative Members: DGUOK (human)UniProtKB:Q16854

Function

deoxyguanosine kinase activityGO:0004138
Substrates: deoxyguanosine / deoxyadenosine / deoxyinosine ATP
Products: dGMP / dAMP / dIMP ADP

Locations

mitochondrial matrixGO:0005759

Purine arm of the mitochondrial deoxyribonucleoside salvage pathway, phosphorylating deoxyguanosine/deoxyadenosine to dNMPs for mtDNA. Deficiency = hepatocerebral mtDNA depletion syndrome (MTDPS3).

Part 3: de novo dNDP supply (p53-inducible ribonucleotide reductase)
ribonucleoside diphosphate (NDP) to 2'-deoxyribonucleoside diphosphate (dNDP)Reactionrrm2b_step

Annotons

RRM2B (p53R2): ribonucleotide reductase small subunit
rrm2b_activity
Participant: Family: Ribonucleotide reductase small subunit family (RRM2/RRM2B)
Family:
Ribonucleotide reductase small subunit family (RRM2/RRM2B)PANTHER:PTHR23409
Representative Members: RRM2B (human, p53R2)UniProtKB:Q7LG56

Function

ribonucleoside-diphosphate reductase activity, thioredoxin disulfide as acceptorGO:0004748
Substrates: ribonucleoside diphosphates (ADP/GDP/CDP/UDP) thioredoxin (reductant)
Products: 2'-deoxyribonucleoside diphosphates (dNDPs)

Locations

cytosolGO:0005829

p53-inducible small subunit of ribonucleotide reductase (with RRM1) providing the de novo dNDP supply for DNA repair and for mtDNA synthesis in quiescent cells. Deficiency = encephalomyopathic mtDNA depletion (MTDPS8) / dominant PEO.

Part 4: thymidine-pool regulation (protects dNTP balance)
thymidine + phosphate <-> thymine + 2-deoxyribose-1-phosphateReactiontymp_step

Annotons

TYMP: thymidine phosphorylase
tymp_activity
Participant: Family: Thymidine/pyrimidine-nucleoside phosphorylase family (TYMP)
Family:
Thymidine/pyrimidine-nucleoside phosphorylase family (TYMP)PANTHER:PTHR10515
Representative Members: TYMP (human)UniProtKB:P19971

Function

thymidine phosphorylase activityGO:0009032
Substrates: thymidine / 2'-deoxyuridine phosphate
Products: thymine / uracil 2-deoxy-alpha-D-ribose 1-phosphate

Locations

cytosolGO:0005829

Cytosolic control of thymidine/deoxyuridine levels; its loss (MNGIE) floods the nucleotide pool with thymidine/deoxyuridine, imbalancing mitochondrial dNTPs and destabilising mtDNA.