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

Eurobic9, 2-6 September, 2008, Wrocław, Poland
O13. Interaction of Zn7metallothionein-2 with Platinum-modified
5’-guanosine Monophosphate (GMP) and DNA
A.V. Karotki, M. Vašák
Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
e-mail: karotki@bioc.unizh.ch
The Cys- and Zn-rich proteins, metallothioneins (Zn7MT), represent a resistance factor in anticancer treatment,
due to the strong reactivity of Pt drugs with S-donor ligands. Previously, we demonstrated that transdichlorodiammineplatinum
(trans-DDP), but not cis-DDP in the reaction with Zn7MT retains the N-donor
ligands [1]. In this study, we show by immunochemical analyses of human MT that platinum-modified DNA
forms DNA−cis-/ trans-Pt−MT cross-links and that in the case of trans-DDP cross-links platinated MT is
released with time. Kinetic studies using cis- and trans-DDP−GMP as a model showed that the initial rate of
the reaction between Zn7MT and cis-DDP−GMP was 4-times higher than the trans-isomer. Quantification of
Pt−S bonds, GMP, and Pt bound to MT revealed one specific binding site for cis-DDP−GMP. In the binding
process the fast initial formation of 2 Pt−S bonds was followed by the slow formation of an additional Pt−S
bond yielding an unusual S3NPt(II) coordination with N7-GMP as the only N-donor. The protein structure,
closely spaced thiolate ligands and noncovalent interactions are likely responsible for the formation of such
complex. In the reaction with trans-DDP−GMP the initial formation of 1 Pt−S bond was followed by a GMP
release, due to the strong trans effect of sulfur, and the formation of a second Pt−S bond. Thus, besides Pt(II)
sequestration, Zn7MT modulates the potency of anticancer drugs through the formation of DNA−Pt−MT crosslinks.
References:
[1] Knipp, M., Karotki, A. V., Chesnov, S., Natile, G., Sadler, P. J., Brabec, V., and Vasak, M. (2007), J. Med.
Chem. 50, 4075−4086.
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