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

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P194. CD and MCD Studies of the Reduced Binuclear Iron Site of
Ribonucleotide Reductase from B. cereus
A.B. Tomter a , C.B. Bell b , A.K. Røhr a , E.I. Solomon b , K.K. Andersson a
a
Department of Molecular Biosciences, University of Oslo, P.O box 1041 Blindern, 0316, Oslo, Norway
e-mail: a.b.tomter@imbv.uio.no
b
Department of Chemistry, Stanford University, 94305, Stanford California, United States
Ribonucleotide reductase (RNR) catalyzes the rate-limiting step in the synthesis deoxyribonucleotides from the
corresponding ribonucleotides needed for DNA synthesis and repair in all living organisms. Class I RNR is
divided into three different classes and they all consist of two non-identical subunits called R1 and R2. The R1
subunit contains the active site, and the R2 subunit a tyrosyl radical and a diiron-oxygen cofactor which are
essential for initiation of the nucleotide reduction process in R1. The R2 subunit of the enzyme complex reacts
with ferrous iron and dioxygen to generate a diferric iron-oxygen cluster and a tyrosyl radical that is essential for
enzymatic activity [1]. The reduced form of the class Ib enzyme, Bacillus cereus R2, has been studied using
a combination of circular dichroism (CD), magnetic circular dichroism (MCD) and variable-temperature
variable-field (VTVH) MCD spectroscopies. Spectral features of individual iron sites have been analyzed to
obtain detailed geometric and electronic structural information. VTVH MCD data have been collected and
analyzed using two complementary models to obtain detailed ground state information including the zero-field
splitting (ZFS) of both ferrous centers and the exchange coupling (J) between the two sites [2]. The results have
been compared to the studies of Escherichia coli R2 [3], mouse R2 [4] and p53R2 [5] which all are of RNR
class 1a.
References:
[1] Kolberg M., Strand K.R., Graff P., Andersson K.K. Biochim. Biophys. Acta- Proteins and Proteomics, 2004,
1699; 1-34.
[2] Solomon, E. I., Brunold, T. C., Davis, M. I., Kemsley, J. N., Lee, S. K., Lehnert, N., Neese, F., Skulan, A. J.,
Yang, Y. S., Zhou, J. Chem. Rev., 2000, 100; 235-349.
[3] Yang, Y.-S., Baldwin, J., Ley, B. A., Bollinger, J. M., Solomon, E. I. J.Am. Chem. Soc. 2000, 122; 8495-
8510.
[4] Strand, K.R., Yang, Y.-S., Andersson, K.K., Solomon, E.I. Biochemistry, 2003, 42; 12223-12234.
[5] Wei P.P, Tomter A.B, Røhr, Å.K. Andersson K.K., Solomon, E.I. Biochemistry, 2006, 45; 14043-14051.
_____________________________________________________________________
313