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

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P186. Metal Site Dynamics on the Nanosecond Time Scale
M. Stachura a , N.J. Christensen b , L. Olsen c , S. Chakraborty d , V.L. Pecoraro d ,
L. Hemmingsen a
a
Department of Natural Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871, Frederiksberg C,
Denmark
e-mail: msta@life.ku.dk
b
Department of Food Science/Quality and Technology, University of Copenhagen, Rolighedsvej 30, 1958,
Frederiksberg C, Denmark
c
Department of Medicinal Chemistry, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen,
Denmark
d
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109 - 1055, United States
Perturbed angular correlation of γ-rays (PAC) spectroscopy is a well establihed technique suitable for
investigation metalloprotein structure [1]. Here we demonstrate that it is also a valuable tool for monitoring the
dynamics occuring at the metal ion binding site on the nanosecond time scale. In the present work the nuclear
quadrupole interactions (NQI) of the 111m Cd derivatives of the de novo designed α-helical peptide TRI
L16CL23A have been investigated in order to monitor the exchange dynamics between and . Only one signal
was observed in Nuclear Magnetic Resonance (NMR) spectroscopy, corresponding to a weighted average of the
two complexes [2]. This suggested that these two structures interconvert rapidly on the NMR timescale (0.01 -
10 ms), whereas in fact they are slow enough to be observed on PAC timescale (0.1 - 100 ns). By carrying out
measurements at several different temperatures, ranging from -196 ºC to 50 ºC, see the figure, the dynamics
changed from slow exchange (at -20 ºC) to intermediate/fast (at 50 ºC) exchange on the PAC time scale.
Exchange rates for the water molecule, and thermodynamic parameters for the reaction have been estimated.
PAC spectra at different temperatures – from slow exchange at -20ºC to intermediate/fast exchange at 50ºC.
References:
[1] Hemmingsen, L., Sas, K. & Danielsen, E. Biological applications of perturbed angular correlations of
gamma-ray spectroscopy. Chem. Rev. 104, 4027-4061(2004).
[2] Matzapetakis M., Farrer B.T., Weng T-C., Hemmingsen L., Penner-Hahn J.E., P ecoraro V.L., Heavy metal
complexation by de novo designed peptides: Comparison of peptid e aggregation preferences in the presence of
cadmium(II), mercury(II) and arsenic(III) J. Am. Chem. Soc. 2002, 124, 8042-8054.
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