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

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P145. The Crystal Structure of the DsrAB Dissimilatory Sulfite Reductase
from D. Vulgaris Bound to DsrC Provides Novel Insights into the
Mechanism of Sulfate Reduction
T.F. Oliveira a , C. Vonrhein b , P.M. Matias a , S.S. Venceslau a , M. Archer a ,
I.A. Cardoso Pereira a
a
Instituto de Tecnologia Química e Biológica/UNL, Av. da República - EAN, 2780-157, Oeiras, Portugal
e-mail: ipereira@itqb.unl.pt
b
Global Phasing Ltd.,Sheraton House, Castle Park, CB3 0AX, Cambridge, United Kingdom
Sulfate reduction is one of the earliest energy metabolisms detected on Earth, at ~3.5 billion years ago [1].
Despite extensive studies, many questions remain about the way respiratory sulfate reduction is associated with
energy conservation [2]. A crucial enzyme in this process is the dissimilatory sulfite reductase (dSiR; DsrAB),
which contains a unique siroheme-[4Fe4S] coupled cofactor, and was present in one of the earliest life forms on
Earth. The number of cofactors of dSiRs is not clear with studies reporting from two to four sirohemes and 10 to
32 non-heme irons per α2β2 module. In Desulfovibrio spp. this protein (desulfoviridin) is particularly intriguing
since it is reported that up to 80% of its siroheme is not metallated but is in the form of sirohydrochlorin, and it
forms a stable complex with DsrC. DsrC is one of the few proteins of the dsr operon to be conserved in both
sulfate/sulfite reducers and sulfur oxidisers. In D. vulgaris DsrC is very highly expressed, at a level twice of
DsrAB [3], pointing to an important role in cellular metabolism.
Here, we report the structure of desulfoviridin from D. vulgaris, in which the dSiR DsrAB subunits form a
complex with DsrC [4]. This structure elucidates several pending questions about desulfoviridin and points to an
essentail role of DsrC in sulfite reduction. We propose a novel mechanism for this reduction that changes our
understanding of sulfate respiration and has important implications for models used to date ancient sulfur
metabolism based on sulfur isotope fractionations.
References:
[1] Y. Shen, R. Buick, D.E. Canfield, Nature, 410, 77 (2001).
[2] P.M. Matias, I.A.C. Pereira, C.M. Soares, M.A. Carrondo, Prog. Biophys. Mol. Biol., 89, 292 (2005).
[3] S.A. Haveman, V. Brunelle, J.K. Voordouw, G. Voordouw, J.F. Heidelberg, R. Rabus, J. Bacteriol., 185,
4345 (2003).
[4] T.F. Oliveira, C. Vonrhein, P.M. Matias, S.S. Venceslau, I.A.C. Pereira, M. Archer, (2008) submitted.
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