Unraveling the Dehaloperoxidase Paradox: Structural, Spectroscopic
and Mechanistic Investigations of Dehaloperoxidase B from Amphitrite
ornata
The enzyme dehaloperoxidase (DHP) from the terebellid polychaete Amphitrite ornata is
a dual-function hemoprotein which, in addition to being the coelomic hemoglobin of the
marine worm Amphitrite ornata, possesses a broad substrate specificity for the oxidative
dehalogenation of environmental haloaromatic toxins such as trihalophenols. As such, DHP
is the first globin identified to possess a biologically relevant peroxidase activity, and thus
provides a unique system to explore our understanding of metalloprotein mechanism,
activation, and design. Using a combination of X-ray diffraction, biochemical assays,
stopped-flow UV-visible, resonance Raman and rapid-freeze-quench electron paramagnetic
resonance spectroscopies, and spectroelectrochemistry, we have elucidated many of the
mechanistic details of DHP isoenzyme B. Our experimental design reveals insights and
kinetic descriptions of the dehaloperoxidase mechanism which have not been previously
reported for isoenzyme A. Namely, we demonstrate a novel reaction pathway in which the
products of the oxidative dehalogenation of trihalophenols (dihaloquinones) are themselves
capable of inducing the formation of oxyferrous DHP B. We further demonstrate that unlike
the traditional monofunctional peroxidases, the oxyferrous state in DHP is a peroxidase
competent starting species, which suggests that the ferric oxidation state may not be an
obligatory starting point for the enzyme. Mutagenesis studies provide evidence for the site(s)
of protein radical formation upon reaction with hydrogen peroxide leading to an updated
catalytic cycle for DHP B. Discussion will focus on the link between the peroxidase and O2transport activities which furthers our understanding of how this bifunctional enzyme is able
to unite its two inherent functions in one system.
Recent publications:
D’Antonio, J.; Ghiladi, R. A. “Reactivity of Deoxy- and Oxyferrous Dehaloperoxidase
B from Amphitrite ornata: Identification of Compound II and its Ferrous-Hydroperoxide
Precursor.” Biochem. 2011, 50, 5999-6011.
D’Antonio, J.; D’Antonio, E. L.; Thompson, M. K.; Bowden, E. F.; Franzen, S.;
Smirnova, T.; Ghiladi, R. A. “Spectroscopic and Mechanistic Investigations of
Dehaloperoxidase B from Amphitrite ornata” Biochem. 2010, 49, 6600-6616.
De Serrano, V.; D’Antonio, J.; Franzen, S.; Ghiladi, R. A. “Structure of
Dehaloperoxidase B at 1.58 Å Resolution and Structural Characterization of the A/B Dimer
from Amphitrite ornata” Acta Cryst. 2010, D66, 529-538.