Histamine modified 2 0 -deoxyriboadenosine – Potential copper binding site in DNAzymes El _ zbieta Lodyga-Chrus ´cin ´ ska a, * , El _ zbieta Sochacka b , Damian Smuga b , Longin Chrus ´cin ´ ski c , Giovanni Micera d , Daniele Sanna e , Monika Turek a , Monika Ga ˛ siorkiewicz a a Institute of General Food Chemistry, Technical University of Lódz ´, ul. Stefanowskiego 4/10, 90-924 Lódz ´, Poland b Institute of Organic Chemistry, Technical University of Lódz ´, ul. _ Zeromskiego 176, 90-924 Lódz ´, Poland c Faculty of Process and Environmental Engineering, Technical University of Lódz ´ ul. Wólczan ´ska 213, 90-924 Lódz ´, Poland d Department of Chemistry, University of Sassari, via Vienna 2, I-07100 Sassari, Italy e Istituto C.N.R. Chim. Biomolecolare, Trav. La Crucca 3, reg. Baldinca, 07040 Sassari, Italy article info Article history: Received 19 November 2009 Received in revised form 19 January 2010 Accepted 21 January 2010 Available online 28 January 2010 Keywords: DNAzymes Histamine modified 2 0 -deoxyriboadenosine Cu(II) complex abstract Copper(II) complexes of histamine modified 2 0 -deoxyriboadenosine (N-[(9-b-D-2 0 -deoxyribofuranosylpu- rin-6-yl)-carbamoyl]histamine) ligand were studied by potentiometric, UV–visible and EPR techniques. The imidazole residue of the ligand was described as the main binding site forming mono-, bis-(ligand) and dimer complexes, but the interactions between adenosine nitrogen N(1) and carbamoyl nitrogen atoms and the copper(II) ion also were detected. This is the first report evaluating the coordinating ability of such a modified adenosine ligand towards copper(II) ion. Our findings suggest that histamine modified 2 0 -deoxyriboadenosine could chelate efficiently copper(II) ions if it were incorporated into DNAzyme sequence. Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction Although DNA has not been found responsible for biological catalysis, many artificial DNA enzymes have been created by ‘‘in vitro selection.” Deoxyribozymes have been made to catalyze DNA phosphorylation [1] and DNA adenylylation [2]. The above mentioned deoxyribozymes are two examples of highly metal-spe- cific DNA enzymes: the former is active only in the presence of Ca(II) and the latter requires Cu(II) for activity. The DNA enzyme ‘‘10–23”, on the other hand, can perform efficient catalysis using many different divalent metal ions [3]. The experimental observa- tions suggest that transition-metal ions may have better ability at creating diverse deoxyribozyme structures [4]. Transition-metal ions may be able to catalyze the reaction, such as phosphodiester transfer or cleavage, more efficiently than for example Mg(II) or Ca(II), because they are better Lewis acids and their metal-bound water possesses a lower pK a , both of which may be important for the reaction. Moreover, transition-metal ions have much richer spectroscopic features than alkaline-earth metal ions, making the study of coordination spheres and reaction mechanisms of metal binding sites in DNAzymes much more fruitful. It has been found that Cu(II) and Mn(II)-derived deoxyribozymes are very specific in metal requirements [4]. This may relate to the ability of transition-metal ions to inter- act in a more covalent fashion with single-stranded DNA mole- cules in constructing catalytic metal binding sites. The findings indicate a strong possibility of engineering very efficient metallo DNA enzymes. The binding of metal ions to DNA is sequence dependent [5,6]. In the minor groove cations localize preferentially at adenine–thy- mine rich sequences, while in the major groove the preferential site is the guanine–cytosine rich sequences [7]. The selected base modified nucleosides can be used as model systems for elucidation of structural and functional features of transition metal ion-specific DNAzymes. The incorporation of imidazole-modified nucleotides can endow DNA with the chemical advantage that histidine provides proteins [8,9]. The modified bases can act indirectly to properly fold the catalytic domain via new H-bonding motifs, electrostatic interactions or hydrophobic effects. Histamine modified 2 0 -deoxyadenosine incorporated into catalytic core of deoxyribozyme ‘‘10–23” was used for the investi- gation of its effect on the DNAzyme catalytic activity [10]. This base will chelate metals to afford appropriate polarization of acceptor in catalytic center. Up till now, no solution studies of equilibrium and structure of copper(II)–imidazole nucleic base complexes have been undertaken. These studies are also indispens- able since the enzymes (DNAzymes) act in biological fluids (mostly aqueous solutions). In many cases real information on coordination stereochemistry, acid–base and metal binding properties can be achieved only by solution studies. 0162-0134/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jinorgbio.2010.01.009 * Corresponding author. Tel.: +48 42 6313417; fax: +48 42 6362860. E-mail address: elalodyg@p.lodz.pl (E. Lodyga-Chrus ´cin ´ ska). Journal of Inorganic Biochemistry 104 (2010) 570–575 Contents lists available at ScienceDirect Journal of Inorganic Biochemistry journal homepage: www.elsevier.com/locate/jinorgbio