Delta24(25)-sterol methenyltransferase: intracellular localization and azasterol sensitivity in Leishmania major promastigotes overexpressing the enzyme.
ABSTRACT Trypanosomatids contain predominantly ergostane-based sterols, which differ from cholesterol, the main sterol in mammalian cells, in the presence of a methyl group in the 24 position. The methylation is initiated by S-adenosyl-L-methionine:Delta(24 (25))-sterol methenyltransferase, an enzyme present in protozoa, but absent in mammals. The importance of this enzyme is underscored by its potential as a drug target in the treatment of the leishmaniases. Here, we report studies concerning the intracellular distribution of sterol methenyltransferase in Leishmania major promastigotes and overexpressing cells using a specific antibody raised against highly purified recombinant protein. It was found by immunofluorescence and electron microscopy studies that in L. major wild-type cells sterol methenyltransferase was primarily associated to the endoplasmic reticulum. In addition to this location, the protein was incorporated into translucent vesicles presumably of the endocytic pathway. We also found in this study that cells overproducing the enzyme do not have increased resistance to the sterol methenyltransferase inhibitor 22, 26 azasterol.
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ABSTRACT: The isoprenoid biosynthetic pathway is a very complex route that entails multiple steps and generates a high number of end-products that are essential for cell viability such as sterols, dolichols, coenzyme Q, heme and prenylated proteins. In parasites from the Trypanosomatidae family this pathway provides new potential drug targets for exploitation in the search for improved therapies, and indeed compounds such as ketoconazole, aminobisphosphonates or terbinafine have been shown to have antiprotozoal activity both in vitro and in vivo. However, despite the high therapeutic importance of the pathway, the subcellular compartmentalization of the different steps of isoprenoid biosynthesis is not known in detail. Here we have analysed the intracellular location of the enzymes 3-hydroxy-3-methyl-glutaryl Coenzyme A (HMG-CoA) synthase (HMGS) and mevalonate kinase (MVAK) in Leishmania major promastigotes as well as in Trypanosoma brucei procyclic and bloodstream forms. For this purpose we generated specific polyclonal antibodies against both highly purified recombinant proteins and used those in indirect immunofluorescence and digitonin titration experiments. Results show that sterol biosynthesis is distributed in multiple intracellular compartments and provide evidence indicating that in trypanosomatids the production of HMG-CoA from acetyl Coenzyme A and generation of mevalonate occur mainly in the mitochondrion while further mevalonate phosphorylation is almost exclusively located in glycosomes. Furthermore, we have determined that peroxin 2 (PEX2) is involved in efficient targeting of MVAK and that the enzyme is relocated to the cytosol upon depletion of this peroxin involved in glycosomal matrix protein import.International journal for parasitology 10/2008; 39(3):307-14. DOI:10.1016/j.ijpara.2008.08.012 · 3.40 Impact Factor
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ABSTRACT: Sterols are constituents of the cellular membranes that are essential for their normal structure and function. In mammalian cells, cholesterol is the main sterol found in the various membranes. However, other sterols predominate in eukaryotic microorganisms such as fungi and protozoa. It is now well established that an important metabolic pathway in fungi and in members of the Trypanosomatidae family is one that produces a special class of sterols, including ergosterol, and other 24-methyl sterols, which are required for parasitic growth and viability, but are absent from mammalian host cells. Currently, there are several drugs that interfere with sterol biosynthesis (SB) that are in use to treat diseases such as high cholesterol in humans and fungal infections. In this review, we analyze the effects of drugs such as (a) statins, which act on the mevalonate pathway by inhibiting HMG-CoA reductase, (b) bisphosphonates, which interfere with the isoprenoid pathway in the step catalyzed by farnesyl diphosphate synthase, (c) zaragozic acids and quinuclidines, inhibitors of squalene synthase (SQS), which catalyzes the first committed step in sterol biosynthesis, (d) allylamines, inhibitors of squalene epoxidase, (e) azoles, which inhibit C14alpha-demethylase, and (f) azasterols, which inhibit Delta(24(25))-sterol methyltransferase (SMT). Inhibition of this last step appears to have high selectivity for fungi and trypanosomatids, since this enzyme is not found in mammalian cells. We review here the IC50 values of these various inhibitors, their effects on the growth of trypanosomatids (both in axenic cultures and in cell cultures), and their effects on protozoan structural organization (as evaluted by light and electron microscopy) and lipid composition. The results show that the mitochondrial membrane as well as the membrane lining the protozoan cell body and flagellum are the main targets. Probably as a consequence of these primary effects, other important changes take place in the organization of the kinetoplast DNA network and on the protozoan cell cycle. In addition, apoptosis-like and autophagic processes induced by several of the inhibitors tested led to parasite death.Interdisciplinary Perspectives on Infectious Diseases 02/2009; 2009:642502. DOI:10.1155/2009/642502
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ABSTRACT: Plastid acquisition, endosymbiotic associations, lateral gene transfer, organelle degeneracy or even organelle loss influence metabolic capabilities in many different protists. Thus, metabolic diversity is sculpted through the gain of new metabolic functions and moderation or loss of pathways that are often essential in the majority of eukaryotes. What is perhaps less apparent to the casual observer is that the sub-compartmentalization of ubiquitous pathways has been repeatedly remodelled during eukaryotic evolution, and the textbook pictures of intermediary metabolism established for animals, yeast and plants are not conserved in many protists. Moreover, metabolic remodelling can strongly influence the regulatory mechanisms that control carbon flux through the major metabolic pathways. Here, we provide an overview of how core metabolism has been reorganized in various unicellular eukaryotes, focusing in particular on one near universal catabolic pathway (glycolysis) and one ancient anabolic pathway (isoprenoid biosynthesis). For the example of isoprenoid biosynthesis, the compartmentalization of this process in protists often appears to have been influenced by plastid acquisition and loss, whereas for glycolysis several unexpected modes of compartmentalization have emerged. Significantly, the example of trypanosomatid glycolysis illustrates nicely how mathematical modelling and systems biology can be used to uncover or understand novel modes of pathway regulation.Philosophical Transactions of The Royal Society B Biological Sciences 03/2010; 365(1541):831-45. DOI:10.1098/rstb.2009.0259 · 6.31 Impact Factor