Pleiotropic action of parasites: How to be good for the host

Parasites reduce the reproductive output of their hosts, limit their growth, and sometimes even castrate or hill them. Under certain conditions however, a parasitized host may be better off than an uninfected one. Such 'nice' parasites have a 'pleiotropic' action on their hosts. Parasites can be pleiotropic either in space (in which case they have a beneficial effect on the host in one environment while being detrimental in another) or in time (the parasite is beneficial at one stage of the host's development and 'costly' at another stage). Such pleiotropic parasites may constitute the intermediate stage between parasitism and mutualism.     

Biologically related iron-sulfur clusters as reaction centers. Reduction of acetylene to ethylene in systems based on [Fe4S4(SR)4]3-

The possibility that clusters containing the Fe4S4 core unit found in a wide variety of proteins can effect reductive transformations of Fe-S enzyme substrates has been investigated using the reduced synthetic clusters [Fe4S4(SPh)4]3- and acetylene, an alternate nitrogenase substrate. The system [Fe4S4(SPh)4]3-/acetic acid/acetic anhydride in N-methylpyrollidinone at approximately 25 degrees was found to reduce acetylene homogeneously to ethylene, and in the presence of a deuterium source to afford as the principal stereochemical product cis-1,2-C2H2D2. No appreciable reduction was found using the oxidized cluster [Fe4S4(SPh)4]2-. The system is not catalytic and departs from the strict stoichiometry of the reaction, 2[Fe4S4(SPh)4]3- + C2H2 + 2H+ leads to 2 [Fe4S4(SPh)4]2- + C2H4, primarily because of a competing cluster oxidation reaction which could not be eliminated. Based on this reaction ca. 60% conversion of acetylene to ethylene was achieved. A reaction sequence based on absorption and 1H nmr spectral observations and product stereo-chemistry is suggested. The results demonstrate that biologically related, reduced Fe4S4 clusters can effect reduction of at least one Fe-S enzyme substrate, and raise the general possibility of substrate transformation with such clusters as reaction sites in biological systems.     

Queuosine Biosynthesis Is Required for Sinorhizobium meliloti-Induced Cytoskeletal Modifications on HeLa Cells and Symbiosis with Medicago truncatula

Rhizobia are symbiotic soil bacteria able to intracellularly colonize legume nodule cells and form nitrogen-fixing symbiosomes therein. How the plant cell cytoskeleton reorganizes in response to rhizobium colonization has remained poorly understood especially because of the lack of an in vitro infection assay. Here, we report on the use of the heterologous HeLa cell model to experimentally tackle this question. We observed that the model rhizobium Sinorhizobium meliloti, and other rhizobia as well, were able to trigger a major reorganization of actin cytoskeleton of cultured HeLa cells in vitro. Cell deformation was associated with an inhibition of the three major small RhoGTPases Cdc42, RhoA and Rac1. Bacterial entry, cytoskeleton rearrangements and modulation of RhoGTPase activity required an intact S. meliloti biosynthetic pathway for queuosine, a hypermodifed nucleoside regulating protein translation through tRNA, and possibly mRNA, modification. We showed that an intact bacterial queuosine biosynthetic pathway was also required for effective nitrogen-fixing symbiosis of S. meliloti with its host plant Medicago truncatula, thus indicating that one or several key symbiotic functions of S. meliloti are under queuosine control. We discuss whether the symbiotic defect of que mutants may originate, at least in part, from an altered capacity to modify plant cell actin cytoskeleton.     

Fractionation of subcellular membranes of the secretory pathway from the peroxidase-producing white-rot fungus Phanerochaete chrysosporium

Abstract Mycelia from the basidiomycete Phanerochaete chrysosporium , producing lignin and manganese peroxidases, were homogenized and fractionated on a sucrose gradient. The main subcellular fungal membrane fractions were successfully separated. Lipid composition analyses of the isolated membranes as well as associated marker enzymes distribution gave evidence to similarities with membranes originating from plants. Lignin and manganese peroxidases were investigated by immunodetection in subcellular fractions. Our results show that lignin and manganese peroxidases are mainly associated with Golgi apparatus vesicles and, to a lesser extent, with endoplasmic reticulum and light density vesicles, but not with plasma membranes.     

A Chemical Proteomics Approach for the Search of Pharmacological Targets of the Antimalarial Clinical Candidate Albitiazolium in Plasmodium falciparum Using Photocrosslinking and Click Chemistry

Plasmodium falciparum is responsible for severe malaria which is one of the most prevalent and deadly infectious diseases in the world. The antimalarial therapeutic arsenal is hampered by the onset of resistance to all known pharmacological classes of compounds, so new drugs with novel mechanisms of action are critically needed. Albitiazolium is a clinical antimalarial candidate from a series of choline analogs designed to inhibit plasmodial phospholipid metabolism. Here we developed an original chemical proteomic approach to identify parasite proteins targeted by albitiazolium during their native interaction in living parasites. We designed a bifunctional albitiazolium-derived compound (photoactivable and clickable) to covalently crosslink drug–interacting parasite proteins in situ followed by their isolation via click chemistry reactions. Mass spectrometry analysis of drug–interacting proteins and subsequent clustering on gene ontology terms revealed parasite proteins involved in lipid metabolic activities and, interestingly, also in lipid binding, transport, and vesicular transport functions. In accordance with this, the albitiazolium-derivative was localized in the endoplasmic reticulum and trans-Golgi network of P. falciparum. Importantly, during competitive assays with albitiazolium, the binding of choline/ethanolamine phosphotransferase (the enzyme involved in the last step of phosphatidylcholine synthesis) was substantially displaced, thus confirming the efficiency of this strategy for searching albitiazolium targets.