PubMed Health⌕ Search

Biomedical subjects

Katja Becker

Publications and source records attributed to Katja Becker.

59 records · Page 4Linked to original sources
PubMed2002

Glutathione S-transferase of the malarial parasite Plasmodium falciparum: characterization of a potential drug target.

Glutathione S-transferases (GSTs), which occur abundantly in most organisms, are essentially involved in the intracellular detoxification of numerous substances including chemotherapeutic agents, and thus play a major role in the development of drug resistance. A gene encoding a protein with sequence identity of up to 37% with known GSTs was identified on chromosome 14 of the malarial parasite Plasmodium falciparum. It was amplified using gametocyte cDNA and expressed in Escherichia coli as a hexahistidyl-tagged protein of 26 kDa subunit size. The homodimeric enzyme (PfGST) was found to catalyse the glutathione (GSH)-dependent modification of 1-chloro-2,4-dinitrobenzene and other typical GST substrates such as o-nitrophenyl acetate, ethacrynic acid, and cumene hydroperoxide. The Km value for GSH was 164+/-20 microM. PfGST was inhibited by cibacron blue (Ki=0.5 microM), S-hexylglutathione (Ki=35 microM), and protoporphyrin IX (Ki=10 microM). Hemin, a most toxic compound for parasitised erythrocytes, was found to be an uncompetitive ligand of PfGST with a Ki of 6.5 microM. Based on the activity of PfGST in extracts of P. falciparum, the enzyme represents 1 to 10% of cellular protein and might therefore serve as an efficient in vivo buffer for parasitotoxic hemin. Destabilising ligands of GST are thus expected to be synergistic with the antimalarial drug chloroquine, which itself was found to be a very weak inhibitor of PfGST (IC50>200 microM). X-ray quality crystals of PfGST (250x200x50 microm) will serve as starting point for structure-based drug design.

Amino Acid Sequence↗
PubMed2001

Crystal structure of the antioxidant enzyme glutathione reductase inactivated by peroxynitrite.

As part of our studies on the nitric oxide-related pathology of cerebral malaria, we show that the antioxidative enzyme glutathione reductase (GR) is inactivated by peroxynitrite, with GR from the malarial parasite Plasmodium falciparum being more sensitive than human GR. The crystal structure of modified human GR at 1.9-A resolution provides the first picture of protein inactivation by peroxynitrite and reveals that this is due to the exclusive nitration of 2 Tyr residues (residues 106 and 114) at the glutathione disulfide-binding site. The selective nitration explains the impairment of binding the peptide substrate and thus the nearly 1000-fold decrease in catalytic efficiency (k(cat)/K(m)) of glutathione reductase observed at physiologic pH. By oxidizing the catalytic dithiol to a disulfide, peroxynitrite itself can act as a substrate of unmodified and bisnitrated P. falciparum glutathione reductase.

Animals↗
PubMedDate not supplied

Thioredoxin networks in the malarial parasite Plasmodium falciparum.

The intraerythrocytic protozoan parasite Plasmodium falciparum is responsible for more than 500 million clinical cases of tropical malaria annually. Although exposed to high fluxes of reactive oxygen species, Plasmodium lacks the antioxidant enzymes catalase and glutathione peroxidase. Thus, the parasite depends on the antioxidant capacity of its host cell and its own peroxidases. These are fuelled by the thioredoxin system and are considered to represent the major defense line against peroxides. Five peroxidases that act in different compartments have been described in P. falciparum. They include two typical 2-Cys peroxiredoxins (Prx), a 1-Cys Prx, the so-called antioxidant protein (AOP), which is a further Prx acting on the basis of a 1-Cys mechanism, and a glutathione peroxidase-like thioredoxin peroxidase. Because of their central function in redox regulation and antioxidant defense, some of these proteins might represent highly interesting targets for structure-based drug development. In this article we summarize the present knowledge on the thioredoxin and peroxiredoxin metabolism in malaria parasitized red blood cells. We furthermore report novel data on the biochemical and kinetic characterization of different thioredoxins, of AOP, and of the classic 1-Cys peroxiredoxin of P. falciparum.

Amino Acid Sequence↗