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

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P15. Ca 2+ and Zn 2+ Modulate the Conformation and Stability of the S100A2
Tumor Suppressor
H. M. Botelho a , M. Koch b , G. Fritz b , C. M. Gomes a
a Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal
b Department of Biology, University of Konstanz, Germany
The S100 proteins are small Ca 2+ binding proteins which regulate processes such as cell cycle, growth,
differentiation and mobility in vertebrates [1]. Human S100A2 binds and activates tumor suppressor p53 in a
Ca 2+ dependent manner [2]. It is an homodimer containing two Ca 2+ and two Zn 2+ binding sites per subunit: Ca 2+
binds at the EF-hands exposing a docking site for downstream signaling proteins; Zn 2+ binds at two surface sites
and regulates the oligomeric state and Ca 2+ affinity in an unique manner in the S100 family [3]. The molecular
determinants for such regulation are currently unknown. The conformation and stability changes associated with
metal binding to S100A2, discriminating the contribution of each Zn 2+ site, were investigated by circular
dichroism spectroscopy using variants with none, one or both Zn 2+ sites. Both metals affected the secondary
structure content without changing the overall α-helical fold. The apo wild type S100A2 exhibited an unfolding
free energy (∆GU) of 89.9 kJ/mol and a midpoint transition temperature (Tm) of 58.4ºC. The two metal ions had
opposite effects towards stability, being Ca 2+ a stabilizer and Zn 2+ a destabilizer [4]. This antagonistic effect,
which suggests a synergy between Ca 2+ activation/stabilization and Zn 2+ inactivation/destabilization, supports
the hypothesis in which increased Zn 2+ levels occurring in some cancer cells [5] may promote the progression of
the disease by impairing S100A2 function.
References:
[1] Fritz, G., and Heizmann, C.W. 2004. 3D structures of the calcium and zinc binding S100 proteins. In
Handbook of metalloproteins. (eds. A. Messerschmidt, R. Huber, T. Poulos, and K. Wieghardt). John Wiley &
Sons.
[2] Mueller, A., Schäfer, B.W., Ferrari, S., Weibel, M., Makek, M., Höchli, M., and Heizmann, C.W. 2005. The
calcium-binding protein S100A2 interacts with p53 and modulates its transcriptional activity. J Biol Chem 280:
29186-29193.
[3] Koch, M., Bhattacharya, S., Kehl, T., Gimona, M., Vasak, M., Chazin, W., Heizmann, C.W., Kroneck, P.M.,
and Fritz, G. 2007. Implications on zinc binding to S100A2. Biochim Biophys Acta 1773: 457-470.
[4] Botelho, H.M., Koch, M., Fritz, G., and Gomes, C.M. 2008. Metal ions modulate the folding and stability of
the tumor suppressor S100A2: insights into functional implications. Submitted.
[5] Ionescu, J.G., Novotny, J., Stejskal, V., Latsch, A., Blaurock-Busch, E., and Eisenmann-Klein, M. 2006.
Increased levels of transition metals in breast cancer tissue. Neuro Endocrinol Lett 27 Suppl 1: 36-39.
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