National Center for
4YOT: Crystal Structure Of A Trimeric Exonuclease Phoexo I From Pyrococcus Horikoshii Ot3 At 2.15a Resolution
Structural basis for substrate recognition and processive cleavage mechanisms of the trimeric exonuclease PhoExo I
Nucleic Acids Res. (2015) 43 p.7122-7136
Nucleases play important roles in nucleic acid processes, such as replication, repair and recombination. Recently, we identified a novel single-strand specific 3'-5' exonuclease, PfuExo I, from the hyperthermophilic archaeon Pyrococcus furiosus, which may be involved in the Thermococcales-specific DNA repair system. PfuExo I forms a trimer and cleaves single-stranded DNA at every two nucleotides. Here, we report the structural basis for the cleavage mechanism of this novel exonuclease family. A structural analysis of PhoExo I, the homologous enzyme from P. horikoshii OT3, showed that PhoExo I utilizes an RNase H-like active site and possesses a 3'-OH recognition site approximately 9 A away from the active site, which enables cleavage at every two nucleotides. Analyses of the heterotrimeric and monomeric PhoExo I activities showed that trimerization is indispensable for its processive cleavage mechanism, but only one active site of the trimer is required.