Methanothermobacter thermautotrophicus Mth212-like subfamily of the ExoIII family purinic/apyrimidinic (AP) endonucleases
This subfamily includes the thermophilic archaeon Methanothermobacter thermautotrophicus Mth212and related proteins. These are Escherichia coli exonuclease III (ExoIII)-like AP endonucleases and they 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, and this is followed by the coordinated actions of DNA polymerase, deoxyribose phosphatase, and DNA ligase. If left unrepaired, AP sites block DNA replication, and have both mutagenic and cytotoxic effects. AP endonucleases can carry out a variety 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. Mth212 is an AP endonuclease, and a DNA uridine endonuclease (U-endo) that nicks double-stranded DNA at the 5'-side of a 2'-d-uridine residue. After incision at the 5'-side of a 2'-d-uridine residue by Mth212, DNA polymerase B takes over the 3'-OH terminus and carries out repair synthesis, generating a 5'-flap structure that is resolved by a 5'-flap endonuclease. Finally, DNA ligase seals the resulting nick. This U-endo activity shares the same catalytic center as its AP-endo activity, and is absent from other AP endonuclease homologues.
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 the 3'-end of one strand of DNA oligonucleotide, a phosphate, and Mg; contacts at 4A
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