Escherichia coli exonuclease III (ExoIII)-like apurinic/apyrimidinic (AP) endonucleases
The ExoIII family AP endonucleases belong to the large EEP (exonuclease/endonuclease/phosphatase) superfamily that contains functionally diverse enzymes that share a common catalytic mechanism of cleaving phosphodiester bonds. AP endonucleases participate in the DNA base excision repair (BER) pathway. AP sites are one of the most common lesions in cellular DNA. During BER, the damaged DNA is first recognized by DNA glycosylase. AP endonucleases then catalyze the hydrolytic cleavage of the phosphodiester bond 5' to the AP site, which is then followed by the coordinated actions of DNA polymerase, deoxyribose phosphatase, and DNA ligase. If left unrepaired, AP sites block DNA replication, which have both mutagenic and cytotoxic effects. AP endonucleases can carry out a wide range of excision and incision reactions on DNA, including 3'-5' exonuclease, 3'-deoxyribose phosphodiesterase, 3'-phosphatase, and occasionally, nonspecific DNase activities. Different AP endonuclease enzymes catalyze the different reactions with different efficiences. Many organisms have two functional AP endonucleases, for example, APE1/Ref-1 and Ape2 in humans, Apn1 and Apn2 in bakers yeast, Nape and NExo in Neisseria meningitides, and exonuclease III (ExoIII) and endonuclease IV (EndoIV) in Escherichia coli. Usually, one of the two is the dominant AP endonuclease, the other has weak AP endonuclease activity, but exhibits strong 3'-5' exonuclease, 3'-deoxyribose phosphodiesterase, and 3'-phosphatase activities. Class II AP endonucleases have been classified into two families, designated ExoIII and EndoIV, based on their homology to the Escherichia coli enzymes. This family contains the ExoIII family; the EndoIV family belongs to a different superfamily.
Comment:based on similarity to ExoIII-like AP endonuclease and other EEP superfamily members; compared with other EEP superfamily members, members of this family have a conserved Tyr residue is in place of a conserved His
Structure:3G4T: Methanothermobacter thermautotrophicus Mth212 binds a dsDNA oligonucleotide with a terminal 5'-phosphate group and a free phosphate anion (contacts at 4A), and a Mg2+ ion
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