Purification and identification of a fatty acyl-CoA synthetase from Trypanosoma brucei

Fatty acid uptake in Trypanosoma brucei: Host resources and possible mechanisms

Trypanosoma brucei spp. causes African Sleeping Sickness in humans and nagana, a wasting disease, in cattle. As T. brucei goes through its life cycle in its mammalian and insect vector hosts, it is exposed to distinct environments that differ in their nutrient resources. One such nutrient resource is fatty acids, which T. brucei uses to build complex lipids or as a potential carbon source for oxidative metabolism. Of note, fatty acids are the membrane anchoring moiety of the glycosylphosphatidylinositol (GPI)-anchors of the major surface proteins, Variant Surface Glycoprotein (VSG) and the Procyclins, which are implicated in parasite survival in the host. While T. brucei can synthesize fatty acids de novo, it also readily acquires fatty acids from its surroundings. The relative contribution of parasite-derived vs. host-derived fatty acids to T. brucei growth and survival is not known, nor have the molecular mechanisms of fatty acid uptake been defined. To facilitate experimental inquiry into these important aspects of T. brucei biology, we addressed two questions in this review: (1) What is known about the availability of fatty acids in different host tissues where T. brucei can live? (2) What is known about the molecular mechanisms mediating fatty acid uptake in T. brucei? Finally, based on existing biochemical and genomic data, we suggest a model for T. brucei fatty acid uptake that proposes two major routes of fatty acid uptake: diffusion across membranes followed by intracellular trapping, and endocytosis of host lipoproteins.

Lipid metabolism in Trypanosoma brucei

Trypanosoma brucei membranes consist of all major eukaryotic glycerophospholipid and sphingolipid classes. These are de novo synthesized from precursors obtained either from the host or from catabolised endocytosed lipids. In recent years, substantial progress has been made in the molecular and biochemical characterisation of several of these lipid biosynthetic pathways, using gene knockout or RNA interference strategies or by enzymatic characterization of individual reactions. Together with the completed genome, these studies have highlighted several possible differences between mammalian and trypanosome lipid biosynthesis that could be exploited for the development of drugs against the diseases caused by these parasites.

A novel 78-kDa fatty acyl-CoA synthetase (ACS1) of Babesia bovis stimulates memory CD4+ T lymphocyte responses in B. bovis-immune cattle

Antigen-specific CD4+ T lymphocyte responses contribute to protective immunity against Babesia bovis, however the antigens that induce these responses remain largely unknown. A proteomic approach was used to identify novel B. bovis antigens recognized by memory CD4+ T cells from immune cattle. Fractions obtained from merozoites separated by continuous-flow electrophoresis (CFE) that contained proteins ranging from 20 to 83 kDa were previously shown to stimulate memory CD4+ lymphocyte responses in B. bovis-immune cattle. Expression library screening with rabbit antiserum raised against an immunostimulatory CFE fraction identified a clone encoding a predicted 78 kDa protein. BLAST analysis revealed sequence identity of this B. bovis protein with Plasmodium falciparum fatty acyl coenzyme A synthetase (ACS) family members (PfACS1-PfACS11), and the protein was designated B. bovis acyl-CoA synthetase 1 (ACS1). Southern blot analysis indicated that B. bovis ACS1 is encoded by a single gene, although BLAST analysis of the preliminary B. bovis genome sequence identified two additional family members, ACS2 and ACS3. Peripheral blood lymphocytes and CD4+ T cell lines from B. bovis-immune cattle proliferated significantly against recombinant ACS1 protein, consistent with its predicted involvement in protective immunity. However, immune sera from cattle recovered from B. bovis infection did not react with ACS1, indicating that epitopes may be conformationally dependent.