Biochemical characterization and mutational analysis of the NurA protein from the hyperthermophilic euryarchaeon Thermococcus barophilus Ch5
Résumé
Archaeal NurA protein plays a key role in producing 3′-single stranded DNA used for homologous recombination repair, together with HerA, Mre11, and Rad50. Herein, we describe biochemical characteristics and roles of key amino acid residues of the NurA protein from the hyperthermophilic euryarchaeon Thermococcus barophilus Ch5 (Tba-NurA). Tba-NurA possesses 5′-3′ exonuclease activity for degrading DNA, displaying maximum efficiency at 45 o C ~ 65 o C and at pH 8.0 in the presence of Mn 2+. The thermostable Tba-NurA also possesses endonuclease activity capable of nicking plasmid DNA and circular ssDNA. Mutational data demonstrate that residue D49 is essential for exonuclease activity and is involved in binding ssDNA since the D19A mutant lacked exonuclease activity and reduced ssDNA binding. No detectable dsDNA binding of the R96A and R129A mutants suggests that residues R96 and R129 are important for binding dsDNA. Since the D120A mutant had no degradation activity and reduced dsDNA binding, residue D120 is essential for degradation activities, and dsDNA binding. Additionally, residues Y392 and H400 are important for exonuclease activity since the mutations lead to exonuclease activity loss. To our knowledge, it is the first report on biochemical characterization and mutational analysis of the NurA protein from Thermococcus.
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