TATDN3

TATDN3 is a divalent metal-dependent DNA nuclease that catalyzes AP (apurinic/apyrimidinic) endonuclease activity on double-stranded DNA and 3'-5' exonuclease activity on single-stranded DNA, with both activities requiring Mg2+ or Mn2+ cofactors (PMID:36881763). The two activities are differentially regulated by the metal identity, as certain divalent metals support AP endonuclease cleavage while inhibiting the exonuclease function (PMID:36881763). Catalysis proceeds through a two-metal ion mechanism, and active-site residues distinguishing the nuclease behavior of TATDN3 from its paralog TATDN1 have been mapped (PMID:36881763). Beyond this in vitro enzymatic characterization, no cellular pathway, substrate context, or in vivo role for TATDN3 has been established in the available corpus.

1. 2023 High

   Whether TATDN3 possesses nuclease activity and on what substrates was unknown; reconstitution with purified protein established it as a metal-dependent enzyme acting on both double- and single-stranded DNA.

   Evidence In vitro nuclease assays with purified recombinant TATDN3 and biochemical characterization of metal cofactor requirements

   PMID:36881763

   Open questions at the time

   • No in vivo or cellular substrate or pathway context established
   • Physiological relevance of the AP endonuclease and exonuclease activities not demonstrated
   • Subcellular localization not determined
2. 2023 Medium

   How TATDN3 achieves catalysis and how it differs from its paralog was unclear; mutagenesis and a paralog crystal structure pointed to a two-metal ion mechanism and identified residues differentiating TATDN1 from TATDN3.

   Evidence Active-site mutagenesis and crystal structure of the paralog TATDN1 bound to dAMP, with biochemical comparison to TATDN3

   PMID:36881763

   Open questions at the time

   • Structural data derive from the paralog TATDN1, not TATDN3 itself
   • No experimental structure of TATDN3 with substrate or metal
   • Mechanistic inference to TATDN3 rests on biochemical analogy

• The cellular and physiological role of TATDN3 — its DNA repair or processing pathway, in vivo substrates, regulation, and localization — remains undefined.
• No cellular phenotype or loss-of-function study in the corpus
• No identified pathway partners or recruitment mechanism
• No demonstrated role in DNA repair in cells