Evidences of a natively unfolded state for the human topoisomerase IB N-terminal domain

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  • Oscar Vassallo, University of Rome Tor Vergata, Italy
  • Silvia Castelli, University of Rome Tor Vergata, Italy
  • Ilda D'Annessa, University of Rome Tor Vergata, Italy
  • Blsco Morozzo della Rocca, University of Rome Tor Vergata, Italy
  • Lorenzo Stella, University of Rome Tor Vergata, Italy
  • Birgitta R. Knudsen
  • Alessandro Desideri, Denmark
The N-terminal domain of human topoisomerase IB has been expressed, purified and characterized by spectroscopic techniques. CD spectra as a function of concentration and pH indicate that the domain does not possess any defined secondary structure. The protein is probably in a natively unfolded state since its denaturation curve is indicative of a non-cooperative transition. Evidence of a partially folded structure comes from the fluorescence spectrum of ANS, whose intensity increases in presence of the domain. Indication of a partial structural arrangement of the domain comes also from the endogenous fluorescence of tryptophans that is centred at 350 nm in the native and shifts to 354 nm in the fully denaturated protein. Interestingly despite the poor structural degree, as also confirmed by a predictive approach, the domain efficiently binds DNA, suggesting that the absence of a defined 3D structure has a functional meaning that permits the domain to be available for the interaction with different molecular partners.
Original languageEnglish
JournalAmino Acids
Pages (from-to)945-953
Number of pages9
Publication statusPublished - 1 Oct 2011

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