TWNK (Twinkle mtDNA helicase) - manual literature synthesis

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Identity and family

• Human TWNK (C10orf2, PEO1; UniProt Q96RR1, 684 aa) encodes Twinkle, the replicative
  DNA helicase of mitochondria. It is a superfamily 4 (SF4), DnaB-like ring helicase
  related to bacteriophage T7 gene 4 primase-helicase PMID:17324440.
• Domain architecture: N-terminal zinc-binding-like domain (ZBD) and RNA-polymerase-like
  domain (RPD; primase-like, catalytically inactive), linker, and C-terminal RecA-like
  helicase/hexamerization domain PMID:25824949. The primase-like domain has lost primase activity PMID:18039713.

Molecular function

• 5'->3' DNA helicase driven by NTP hydrolysis (UTP optimal) [PMID:12975372 "TWINKLE is a
  DNA helicase with 5' to 3' directionality and distinct substrate requirements"; "The
  helicase activity has an absolute requirement for hydrolysis of a nucleoside
  5'-triphosphate, with UTP being the optimal substrate."].
• Unwinding stimulated by mtSSB (SSBP1) PMID:12975372.
• Binds ssDNA (N-terminal region required) and also dsDNA [PMID:18039713 "the N-terminal
  part of TWINKLE is required for efficient binding to single-stranded DNA"; "In contrast
  to the phage protein, TWINKLE binds to double-stranded DNA."].
• Also has strand-annealing activity PMID:22383523, D-loop dissociation and
  branch migration PMID:27226550.
• Oligomeric state: hexamers (and heptamers/higher oligomers) formed without nucleotide
  PMID:18039713;
  PMID:22383523.
• Membrane association: full-length human Twinkle and its RPD bind cardiolipin-containing
  liposomes; ATPase is stimulated by liposomes PMID:34950192.

Biological process

• Replicative helicase of the mtDNA replisome with POLG and mtSSB; in vitro reconstitution
  PMID:15167897.
• Mouse conditional knockout: TWINKLE is the only replicative helicase in mammalian
  mitochondria and is required for nascent D-loop H-strand synthesis PMID:23393161.
• In cells, dominant adPEO mutants cause replication stalling and mtDNA depletion
  PMID:18971204. A reduction in
  mitochondrial transcripts was also seen, but this is a downstream consequence, not
  evidence that Twinkle participates in transcription PMID:18971204.
• Loading of TWINKLE at the D-loop 3' end (coreTAS) by ChIP PMID:26253742.
• Drosophila models of the orthologous helicase: dominant-negative active-site and adPEO
  mutations deplete mtDNA, cause OXPHOS defects and secondary apoptosis PMID:22952820. Apoptosis
  is an indirect consequence, not a Twinkle function.

Location

• Mitochondrial nucleoids (co-localizes with mtDNA) PMID:18971204; co-fractionates with
  mtDNA PMID:23275553; nucleoids associate with the inner membrane PMID:34950192.

Interactions

• Co-IP with LONP1 PMID:14739292; Twinkle is a LONP1
  substrate according to Reactome R-HSA-9838081.
• High-throughput Y2H hits (LGALS3BP) from HuRI/BioPlex-type screens (PMID:28514442,
  PMID:33961781) have no functional follow-up.

Disease

• adPEO with multiple mtDNA deletions (PEOA3), MTDPS7 (infantile-onset spinocerebellar
  ataxia / hepatocerebral), Perrault syndrome 5 (UniProt Q96RR1 DISEASE).

Isoforms

• Isoform 2 (Twinky) lacks ATPase/unwinding and DNA binding and is monomeric (UniProt
  Q96RR1 FUNCTION [Isoform 2], citing PMID:18039713).