Impact of the Oxidized Guanine Lesion Spiroiminodihydantoin on the Conformation and Thermodynamic Stability of a 15-mer DNA Duplex†

Fadzai Chinyengetere and Elizabeth R. Jamieson*
Department of Chemistry, Smith College, Northampton, Massachusetts 01063
Biochemistry, 2008, 47 (8), pp 2584–2591
DOI: 10.1021/bi701502t
Publication Date (Web): February 19, 2008
Copyright © 2008 American Chemical Society
†

 Funding for this work was provided by Smith College (Tomlinson Fund and Howard Hughes Medical Institute Awards to F.C., Start-up Funds and CFCD Awards to E.R.J.). Mass spectral data were obtained at the University of Massachusetts Mass Spectrometry Facility, which is supported, in part, by the National Science Foundation.

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*

 To whom correspondence should be addressed. Phone:  (413) 585-7588. Fax:  (413) 585-3786. E-mail:  ejamieso@email.smith.edu.

Abstract

Abstract Image

Spiroiminodihydantoin (Sp) is a hyperoxidized guanine base produced from oxidation of the mutagenic DNA lesion 7,8-dihydro-8-oxo-2‘-deoxguanosine (8-oxoG) by a variety of species including peroxynitrite, singlet oxygen, and the high-valent metals Ir(IV) and Cr(V). In this study, the conformation and thermodynamic stability of a 15-mer DNA duplex containing an Sp lesion are examined using spectroscopic techniques and differential scanning calorimetry (DSC). The Sp lesion does not alter the global B-form conformation of the DNA duplex as determined by circular dichroism spectroscopy. Thermal denaturation experiments find that Sp significantly lowers the thermal stability of the duplex by 20 °C. The enthalpies, entropies, and free energies of duplex formation for 15-mers containing guanine, 8-oxoG, and Sp were determined by performing DSC experiments as well as van't Hoff analysis of UV melting spectroscopic data. The thermodynamic stability of the Sp duplex is significantly reduced compared to that of both the 8-oxoG and parent G duplexes, with the thermodynamic destabilization being enthalpic in origin. The thermodynamic impact of the Sp lesion is compared to what is found for other types of DNA base damage and discussed in relation to how the presence of this lesion could affect cellular processes, in particular the recognition and repair of these adducts by the base excision repair enzymes.

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History

  • Published In Issue February 26, 2008
  • Received July 27, 2007
    Revised Manuscript Received November 2, 2007

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