Research Group Heussler (Malaria I) - Bernhard-Nocht-Institut für ...

Parasitology Section
Structural analysis of the glutathione S-transferase
from Plasmodium falciparum
Zusammenfassung
Ein Hauptmechanismus xenobiotischer/antioxidativer
Abwehrsysteme basiert auf der Glutathion-
Konjugation, katalysiert durch die Glutathion S-Transferasen
(GSTs). Plasmodium falciparum, der Erreger
der Malaria tropica, besitzt eine einzige GST, der somit
eine zentrale Rolle in der Detoxifikation zukommt.
Ihre selektive und spezifische Inhibition stellt einen
aussichtsreichen Ansatzpunkt für eine rationale
Wirkstoffentwicklung dar. Durch die Klonierung und
rekombinante Expression der GST von P. falciparum
(Pf-GST) wurden Voraussetzungen zur Kristallisation
und Röntgenstrukturanalyse des Proteins geschaffen.
Die Pf-GST wurde sowohl mit als auch ohne den
Inhibitor S-Hexylglutathion kristallisiert und ihre 3D-
Struktur konnte mittels Röntgenbeugungsanalyse
unter Anwendung von Synchrotronstrahlung aufgeklärt
werden. Die erhaltenen Strukturdaten liefern
eine wichtige Grundlage für die strukturbasierende
Entwicklung neuer Antimalaria-Medikamente.
Summary
Glutathione S-transferases (GSTs) are involved in the
detoxification of endogenous and xenobiotic compounds
using either glutathione conjugation, glutathione
peroxidase activity or passive/sacrificial binding.
The critical role played by the sole GST of Plasmodium
falciparum (Pf-GST) in detoxification makes it
a viable drug target against malaria. For high-resolution
crystallographic investigations, GST was overexpressed
in bacterial cells and was crystallized in the native form
and with the inhibitor S-hexylglutathione. By X-ray
crystallography using synchrotron radiation, the threedimensional
structure of the Pf-GST1 was determined.
The obtained data forms the basis of structure-based
design of selective inhibitors, which may serve as antimalarial
drug leads.
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Introduction
Glutathione S-transferases (GSTs; EC 2.5.1.18) are a
major family of detoxification enzymes that are found in
organisms ranging from prokaryotes to mammals. They
catalyse the nucleophilic addition of glutathione to a
large variety of electrophilic substrates, thereby detoxifying
both endobiotic and xenobiotic compounds. Besides
catalyzing conjugation reactions, GSTs can also
reduce organic hydroperoxides of phospholipids, fatty
acids and DNA before they become engaged in freeradical
propagation reactions, ultimately leading to the
destruction of macromolecules during oxidative stress.
In addition to their enzymatic functions, GSTs have
been shown to serve in structural roles (S-crystallins) or
act as regulatory proteins. For example, GSTs are involved
in the sequestering and transport of exogenous
potentially toxic compounds such as pesticides, herbicides
and antibiotics and have been shown to bind a
large variety of endogenous compounds such as
steroids, bilirubin, bile acids and ferriprotoporphyrin IX
with high to moderate affinities. Within a parasitic context,
it is especially important to consider their function
in the regulation of oxidative stress response, in drug
resistance and possibly in the modulation of host
immune defense mechanisms.
Figure 1: Initial small crystals of Pf-GST. (b) Crystals after optimization
with dimensions of up to 0.4 x 0.4 x 0.3 mm.