ISBN: 978-83-60043-10-3 - eurobic9

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Eurobic9, 2-6 September, 2008, Wrocław, Poland P99. NMR Investigations of Cobalt(III)-hexammine Coordination to Domain 6 of a Group II Intron Ribozyme M.M.T. Korth a , M.C. Erat b , R.K.O. Sigel a a Institute of Inorganic Chemistry, University of Zurich, Winterthurerstr. 190, 8057, Zurich, Switzerland e-mail: maximiliane.korth@aci.uzh.ch b Department of Biochemistry, University of Oxford, South Parks Road, OX1 3QU, Oxford, United Kingdom Group II intron ribozymes are large self-splicing RNA molecules that have a highly conserved secondary structure of six individual domains projecting from a central wheel (see Figure). Domain 6 (D6) contains a conserved adenosine (the branch point) whose 2'-OH acts as the nucleophile in the first step of splicing. Mg 2+ plays an essential role for the folding into the three-dimensional structure and the catalytic activity of ribozymes. [1] The NMR solution structure of a 27 nucleotide long D6 construct (D6-27) that supports catalysis was recently elucidated [2] and its intrinsic Mg 2+ binding properties were determined. [3] One Mg 2+ thereby binds at the branch region. Here we investigate possible outersphere coordination of this Mg 2+ ion in the branch region of D6-27. Cobalt(III)-hexammine is a commonly used mimic for the spectroscopically silent [Mg(H2O)6] 2+ in NMR studies and can even show NOE contacts with RNA protons in favorable cases. [Co(NH3)6] 3+ titration experiments were performed in H2O and D2O observing the chemical shift changes of the RNA protons. Chemical shift mapping shows distinct binding of [Co(NH3)6] 3+ to the branch region of D6-27. Furthermore direct NOE contacts between the ammine protons of [Co(NH3)6] 3+ and RNA protons are detected, providing proton-proton distances for structural calculations to elucidate the geometry of [Mg(H2O)6] 2+ coordination to the branchpoint. Acknowledgement: Financial support by the Swiss National Science Foundation (SNF-Förderungsprofessur PP002-114759 to R.K.O.S.) is gratefully acknowledged References: [1] R. K. O. Sigel, Eur. J. Inorg. Chem., 2005, 12, 2281-2292. [2] M. C. Erat, O. Zerbe, T. Fox, R. K. O. Sigel, ChemBioChem, 2007, 8, 306-314. [3] M. C. Erat, R. K. O. Sigel, Inorg. Chem., 2007, 46, 11224-11234. _____________________________________________________________________ 218
Eurobic9, 2-6 September, 2008, Wrocław, Poland P<strong>10</strong>0. Binding of MMR Protein MutS to Mispaired DNA Adducts of Intercalating Ru(II) Arene Complexes H. Kostrhunova a , V. Marini a , J. Kasparkova a , P.J. Sadler b , J.-M. Malinge c , V. Brabec a a Institute of Biophysics, AS CR, v.v.i., Kralovopolska 135, 612 65, Brno, Czech Republic, e-mail: kostrhunova@ibp.cz b Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, United Kingdom c Centre de Biophysique Moleculaire, CNRS, Rue Charles Sadron, 45071, Orleans, France We examined the binding properties of Escherichia coli mismatch repair protein MutS with various DNA substrates containing a single centrally located adduct of Ru(II) arene complexes [(eta 6 -arene)Ru(II)(en)Cl][PF6] [arene=tetrahydroanthracene (Ru-THA) or p-cymene (Ru-Cym), en=ethylenediamine]. These complexes were chosen as representatives of two different classes of monofunctional Ru(II)-arene compounds which differ in DNA binding modes: one that involves combined coordination to G N7 along with noncovalent, arene intercalation (tricyclic-ring Ru-THA) and the other that binds to DNA only via coordination to G N7 and does not interact with DNA by intercalation (mono-ring Ru-Cym). Using electrophoretic mobility shift assay, the binding properties of MutS protein with various DNA duplexes (homo- or mismatched duplexes) containing a single centrally-located adduct of Ru(II)-arene compounds were examined. We have shown that presence of Ru(II)-arene adducts decreases the affinity of MutS for ruthenated duplexes that either have a regular sequence or contain a mismatch and that intercalation of the arene considerably contributes to this inhibition effect. Since MutS initiates mismatch repair by recognizing DNA lesions the results of the present work support the view tha DNA damage due to intercalation is removed from DNA by mechanism(s) other than mismatch repair. _____________________________________________________________________ 219
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ISBN: 978-83-60043-10-3 - eurobic9

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