Fine tuning of the catalytic activity of colicin e7 nuclease domain by systematic n-terminal mutations

Eszter Németh, Tamás Körtvélyesi, Peter W. Thulstrup, Hans Erik Mølager Christensen, Milan Kožíšek, Kyosuke Nagata, Aniko Czene, Béla Gyurcsik

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The nuclease domain of colicin E7 (NColE7) promotes the nonspecific cleavage of nucleic acids at its C-terminal HNH motif. Interestingly, the deletion of four N-terminal residues (446–449NColE75KRNK) resulted in complete loss of the enzyme activity. R447A mutation was reported to decrease the nuclease activity, but a detailed analysis of the role of the highly positive and flexible N-terminus is still missing. Here, we present the study of four mutants, with a decreased activity in the following order: NColE7>>KGNK>KGNG~GGNK>GGNG. At the same time, the folding, the metal-ion, and the DNA-binding affinity were unaffected by the mutations as revealed by linear and circular dichroism spectroscopy, isothermal calorimetric titrations, and gel mobility shift experiments. Semiempirical quantum chemical calculations and molecular dynamics simulations revealed that K446, K449, and/or the N-terminal amino group are able to approach the active centre in the absence of the other positively charged residues. The results suggested a complex role of the N-terminus in the catalytic process that could be exploited in the design of a controlled nuclease
Original languageEnglish
JournalProtein Science
Issue number8
Pages (from-to)1113-1122
Publication statusPublished - 2014


  • DNA cleavage
  • Flow linear dichroism
  • Isothermal calorimetry
  • Positively charged N-terminal residues
  • Zn 2 1 binding

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