Unusually wide co-factor tolerance in a metalloenzyme; divalent metal ions modulate endo–exonuclease activity in T5 exonuclease
AUTOR(ES)
Garforth, Scott J.
FONTE
Oxford University Press
RESUMO
T5 5′–3′ exonuclease is a member of a homologous group of 5′ nucleases which require divalent metal co-factors. Structural and biochemical studies suggest that single-stranded DNA substrates thread through a helical arch or hole in the protein, thus bringing the phosphodiester backbone into close proximity with the active site metal co-factors. In addition to the expected use of Mg2+, Mn2+ and Co2+ as co-factors, we found that divalent zinc, iron, nickel and copper ions also supported catalysis. Such a range of co-factor utilisation is unusual in a single enzyme. Some co-factors such as Mn2+ stimulated the cleavage of double-stranded closed-circular plasmid DNA. Such endonucleolytic cleavage of circular double-stranded DNA cannot be readily explained by the threading model proposed for the cleavage of substrates with free 5′-ends as the hole observed in the crystal structure of T5 exonuclease is too small to permit the passage of double-stranded DNA. We suggest that such a substrate may gain access to the active site of the enzyme by a process which does not involve threading.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=55779Documentos Relacionados
- DmGEN, a novel RAD2 family endo-exonuclease from Drosophila melanogaster
- Intracellular localization of Neurospora crassa endo-exonuclease and its putative precursor.
- Purification and characterization of an endo-exonuclease from adult flies of Drosophila melanogaster.
- Neurospora endo-exonuclease is immunochemically related to the recC gene product of Escherichia coli.
- The estimation of heparin co-factor in serum