PubMed Health⌕ Search

Biomedical subjects

R J M Wilson

Publications and source records attributed to R J M Wilson.

7 recordsLinked to original sources
PubMed2005

The plastid of Plasmodium spp.: a target for inhibitors.

Determined efforts are being made to explore the non-photosynthetic plastid organelle of Plasmodium falciparum as a target for drug development. Certain antibiotics that block organellar protein synthesis are already in clinical use as antimalarials. However, all the indications are that these should be used only in combination with conventional antimalarials. The use of antibiotics such as doxycycline and clindamycin may reduce the development of drug resistant parasites and such means to avoid drug resistance should be explored hand-in-hand with drug development. Genomic information predicts that fatty acid type II (FAS II) and isoprenoid biosynthetic pathways are localized to the plastid. However, clinical trials with fosmidomycin (a specific inhibitor of DOXP reductase in the non-mevalonate pathway for isoprenoids) suggest it too should only be used in drug combinations. Prospects for more potent antimalarial compounds have emerged from studies of several of the enzymes involved in the FAS II pathway. Lead antibiotics such as thiolactomycin (an inhibitor of beta-ketoacyl-ACP synthase) and triclosan (a specific inhibitor of enoyl-ACP reductase) have led to structurally similar, active compounds that rapidly kill ring- and trophozoite-stage parasites. The FAS II pathway is of particular interest to the pharma-industry.

Animals↗
PubMed2004

Enzymes for heme biosynthesis are found in both the mitochondrion and plastid of the malaria parasite Plasmodium falciparum.

All eight enzymes required for de novo heme biosynthesis have been predicted from the nuclear genome of the human malaria parasite Plasmodium falciparum. We have studied the subcellular localization of three of these using a GFP reporter in live transfected parasites. The first enzyme in the pathway delta-aminolevulinic acid synthase (ALAS) is targeted to the mitochondrion, but the next two enzymes porphobilinogen synthase (PBGS) and hydroxymethylbilane synthase (HMBS) are targeted to the plastid. An enzymatically active recombinant version of PBGS from P. falciparum was over-expressed and its activity found to be stimulated by Mg2+ (and enhanced by Mn2+) but not by Zn2+. A hypothetical scheme for the exchange of intermediates in heme biosynthesis between the mitochondrion and plastid organelle, as well as organelle attachment is discussed.

5-Aminolevulinate Synthetase↗
PubMed2003

Proteobacteria-like ferrochelatase in the malaria parasite.

A gene encoding the heme biosynthetic enzyme ferrochelatase (FC) was found in the genomic DNA databases of Plasmodium spp. The predicted amino acid sequence of malarial FC is highly conserved and fairly well conserved by comparison with other orthologues. The FC genes of P. falciparum and P. yoelii are transcribed and the mRNAs are processed to encode polypeptides of the expected amino acid sequence. The cloned cDNA for the FC of P. falciparum successfully rescued a FC-null mutant of Escherichia coli, indicating that it encodes an active enzyme. Unlike eukaryotic FCs, the malarial enzyme lacks a characteristic extension at the C-terminus. In addition, the sequence of the malarial FC resembles proteobacterial orthologues rather than eukaryotic enzymes. Strikingly, the malarial FC lacks a bipartite presequence at its N-terminus, unlike delta-aminolevulinic acid dehydratase of the same organism. This suggests an unusual intracellular distribution of heme biosynthetic enzymes, involving multiple subcellular compartments.

Amino Acid Sequence↗
PubMed2002

The genome of Plasmodium falciparum encodes an active delta-aminolevulinic acid dehydratase.

The enzyme delta-aminolevulinic acid dehydratase (ALAD) catalyses the second reaction in the heme biosynthetic pathway. It has been suggested previously that the malaria parasite Plasmodium falciparum imports this enzyme from the host cell for de novo heme biosynthesis. However, the parasite's genome encodes an orthologue for ALAD. Here we report molecular cloning of a complete cDNA for the parasite's intrinsic ALAD and show it rescues an ALAD-null mutant of Escherichia coli, indicating that the malarial gene encodes a functional ALAD. The malarial ALAD has a long bipartite extension at its N-terminus, which may function as a plastid targeting signal. The amino acid sequence of the enzyme is related most closely to those of plant/algal chloroplast ALADs, though the malarial version may lack the allosteric Mg2+-binding site, which is conserved among chloroplast ALADs.

Allosteric Site↗
PubMed2002

The plastid DNA of the malaria parasite Plasmodium falciparum is replicated by two mechanisms.

In common with other apicomplexan parasites, Plasmodium falciparum, a causative organism of human malaria, harbours a residual plastid derived from an ancient secondary endosymbiotic acquisition of an alga. The function of the 35 kb plastid genome is unknown, but its evolutionary origin and genetic content make it a likely target for chemotherapy. Pulsed field gel electrophoresis and ionizing radiation have shown that essentially all the plastid DNA comprises covalently closed circular monomers, together with a tiny minority of linear 35 kb molecules. Using two-dimensional gels and electron microscopy, two replication mechanisms have been revealed. One, sensitive to the topoisomerase inhibitor ciprofloxacin, appears to initiate at twin D-loops located in a large inverted repeat carrying duplicated rRNA and tRNA genes, whereas the second, less drug sensitive, probably involves rolling circles that initiate outside the inverted repeat.

Animals↗