The chemical composition of trypanosomes. I. Protein, amino acid and sugar analysis

Nutrient availability regulates proline/alanine transporters in Trypanosoma brucei

Trypanosoma brucei is a species of unicellular parasite that can cause severe diseases in livestock and humans, including African trypanosomiasis and Chagas disease. Adaptation to diverse environments and changes in nutritional conditions is essential for T. brucei to establish an infection when changing hosts or during invasion of different host tissues. One such adaptation is the ability of T. brucei to rapidly switch its energy metabolism from glucose metabolism in the mammalian blood to proline catabolism in the insect stages and vice versa. However, the mechanisms that support the parasite's response to nutrient availability remain unclear. Using RNAseq and qRT-PCR, we investigated the response of T. brucei to amino acid or glucose starvation and found increased mRNA levels of several amino acid transporters, including all genes of the amino acid transporter AAT7-B subgroup. Functional characterization revealed that AAT7-B members are plasma membrane-localized in T. brucei and when expressed in Saccharomyces cerevisiae supported the uptake of proline, alanine, and cysteine, while other amino acids were poorly recognized. All AAT7-B members showed a preference for proline, which is transported with high or low affinity. RNAi-mediated AAT7-B downregulation resulted in a reduction of intracellular proline concentrations and growth arrest under low proline availability in cultured procyclic form parasites. Taken together, these results suggest a role of AAT7-B transporters in the response of T. brucei to proline starvation and proline catabolism.

The Uptake and Metabolism of Amino Acids, and Their Unique Role in the Biology of Pathogenic Trypanosomatids

Trypanosoma brucei, as well as Trypanosoma cruzi and more than 20 species of the genus Leishmania, form a group of flagellated protists that threaten human health. These organisms are transmitted by insects that, together with mammals, are their natural hosts. This implies that during their life cycles each of them faces environments with different physical, chemical, biochemical, and biological characteristics. In this work we review how amino acids are obtained from such environments, how they are metabolized, and how they and some of their intermediate metabolites are used as a survival toolbox to cope with the different conditions in which these parasites should establish the infections in the insects and mammalian hosts.

The Amino Acid Composition of Anopheles stephensi (Diptera: Culicidae) Infected with Nosema algerae (Microsporida: Nosematidae)

The amino acid composition of larvae, pupae, and adult mosquitoes of Anopheles stephensi infected with Nosema algerae and noninfected insects was analyzed using an amino acid analyzer. The increase and decrease in the concentration of single amino acids during the development of the microsporidium were compared with the spread of meronts, sporonts, and spores within the host. The appearance of meronts and sporonts coincided mainly with an increase in the concentration of alanine and histidine. The amount of alanine, proline, and tyrosine decreased during spore formation. Tyrosine appeared in the hemolymph of infected A. stephensi, whereas this amino acid could not be found in the blood of uninfected insects. The spores themselves contained predominantly the glycogenic amino acid alanine, glutamic acid, aspartic acid, serine, and glycine. Proline, methionine, or tyrosine could not be detected within the spores. Copyright 1998 Academic Press. Copyright 1998 Academic Press

Intermediate metabolism in Trypanosoma cruzi

Epimastigotes of Trypanosoma cruzi, the causative agent of Chagas disease, catabolize proteins and amino acids with production of MH3, and glucose with production of reduced catabolites, chiefly succinate and L-alanine, even under aerobic conditions. This "aerobic fermentation of glucose" is probably due to both the presence of low levels of some cytochromes, causing a relative inefficiency of the respiratory chain for NADH, reoxidation during active glucose catabolism, and the lack of NADH dehydrogenase and phosphorylation site I, resulting in the entry of reduction equivalents into the chain mostly as succinate. Phosphoenol pyruvate carboxykinase and pyruvate kinase may play an essential role in diverting glucose carbon to succinate or L-alanine, and L-malate seems to be the major metabolite for the transport of glucose carbon and reduction equivalents between glycosome and mitochondrion. The parasite contains proteinase and peptidase activities. The major lysosomal cysteine proteinase, cruzipain, has been characterized in considerable detail, and might be involved in the host/parasite relationship, in addition to its obvious role in parasite nutrition. Among the enzymes of amino acid catabolism, two glutamate dehydrogenases (one NADP- and the other NAD-linked), alanine aminotransferase, and the major enzymes of aromatic amino acid catabolism (tyrosine aminotransferase and aromatic alpha-hydroxy acid dehydrogenase), have been characterized and proposed to be involved in the reoxidation of glycolytic NADH.

Biochemistry of the sarcocyst of Sarcocystis fusiformis of buffalo Bubalus bubalis

Sarcocysts of Sarcocystis fusiformis from oesophageal muscles of naturally-infected Indian water buffalo (Bubalus bubalis) were analysed for total lipids, phospholipids, cholesterol, fatty acids and glycerides and total protein. Protein and phospholipids constituted the major portion of the sarcocyst. Acetylcholinesterase and glutamate-oxalo-acetate transaminase activities when assayed were higher than glutamate-pyruvate transaminase in sarcocysts.

Carbohydrate composition of variant-specific surface antigen glycoproteins from Trypanosoma brucei

The carbohydrate of variant-specific surface antigen glycoproteins from bloodstream forms of 13 cloned variants of Trypanosoma brucei was analyzed by gas-liquid chromatography. The glycoproteins contained from 6 to 17% carbohydrate by weight, and all contained the same 4 sugars: mannose, galactose, glucose, and glucosamine (probably as N-acetylglucosamine). The glycoprotein from variant 048, strain 427 contained (+20%) 11 mannose, 4 galactose, 4 glucose, and 5 glucosamine residues/mole of glycoprotein (molecular weight 65,000). Glucose was an intergral component of the glycoproteins, not dissociable by sodium dodecyl sulphate, 8 M urea, or 1 M acetic acid. Some of the glucose was dissociated by trichloroacetic acid. Most of the glycoproteins formed precipitin with concanavalin A in Ouchterlony double diffusion, but none formed such bands with wheat germ agglutinin or Ricinus communis lectin (molecular weight 120, 000).

The cell surface of Trypanosoma musculi bloodstream forms. II. Lectin and immunologic studies

Living Trypanosoma musculi bloodstream trypomastigotes were agglutinated specifically with concanavalin A (ConA), wheat germ agglutinin (WGA), soybean agglutinin (SBA), and fucose-binding protein (FBP). The agglutination with these lectins of living cells from which the coat was removed by trypsinization was the same as with intact trypanosomes. Glutaraldehyde or formalin fixation did not affect the results with regard to agglutination with WGA, SBA, and FBP, but lower agglutination with ConA was observed upon fixation. By using a dense iron-dextran marker many fewer ConA marker particles were localized at the fine structural level in the intact than in trypsin-treated trypanosomes. On the basis of the results obtained by agglutination and electron microscopy, it is likely that fixation cross-links intact surface-coat components associated with the ConA binding sites. It is evident from the studies in which lectins were employed that ligands containing alpha-D-mannose, N-acetylglucosamine, N-acetylgalactosamine, and alpha-L-fucose are randomly distributed in the outer surface of the pellicular and flagellar membranes of T. musculi trypomastigotes. Results obtained with alpha-amylase- and dextranase-treated trypanosomes suggested that lectin-binding sugar ligands in the cell surface were not directly associated with alpha-1,4 or repetitive alpha-1,6 glucan-bonded polysaccharide moieties. Similar conclusions can be drawn on the basis of neuraminidase treatment with regard to N-acetylated neuraminic acids. After thorough washing, intact, but not trypsin-treated trypomastigotes were agglutinated specifically with antisera against whole mouse serum and against mouse IgG. Evidently, adsorbed constituents of mouse serum are regular components of the T. musculi surface coat. After incubation in dilute whole mouse serum or in mouse IgG solutions, also the trypsinized cells were agglutinated by the 2 antisera. No such results were obtained with trypsinized cells incubated in serum-free buffers. It was concluded that mouse serum proteins were readily readsorbed on, and firmly bound to the trypsinized cells' surfaces. Specific agglutinations were obtained with trypsinized cells after incubation in dilute rat, rabbit, bovine, and human sera and in solutions of rat and rabbit IgG in reactions with the corresponding antisera. It seems, therefore, that the host serum proteins are adsorbed nonspecifically to the cell surface of trypsinized T. musculi bloodstream forms. When examined by electron microscopy, the intact trypomastigotes were covered by an ununiform, slightly granular, fibrillar extracellular coat, applied to the entire outer lamina of the pellicular and flagellar membranes. No indication of such a coat was noted in the trypsinized organisms. Flocculent surface coat-like matrix could, however, be discerned in cells which, after trypsinization, were incubated in various sera.

Monosaccharide composition of the surface glycoprotein antigens of Trypanosoma brucei

Evidence has been adduced that the surface antigens ofTrypanosoma bruceisubgroup are a group of glycoproteins having D-galactose, D-mannose and D-glucosamine as monosaccharide components.

There was considerable variation in the number of antigen components, and their relative amounts, as revealed by isoelectric focusing on polyacrylamide gel. The relevance of these variations to the adaptation theory of antigenic variation in trypanosomes is discussed.

Short-interval absorption and metabolism of some amino acids in Trypanosoma gambiense

During 2 min incubations of Trypanosoma gambiense (bloodstream form) with [U-14C]glucose (1 mM) over 60% of absorbed label was detected in free alanine. In the presence of 12·5 mM unlabelled alanine, the amount of alanine synthesized from glucose was reduced by less than 10%. These data support previous observations on the high level of transaminase activity in African human trypanosomes.

Alanine, aspartate and glutamate were metabolized to various other free amino acids whereas a significant amount of label derived from [14C]arginine could not be accounted for by amino acid assay.

The sulphur containing amino acids, cysteic acid and taurine, were apparently synthesized from alanine, glutamate and arginine. The significance of these syntheses is poorly understood.

Following incubations of trypanosomes for 2 min in exogenous amino acids the internal free pool became imbalanced due to accumulation and metabolism of the substrate amino acid.

Evidence obtained indicated that the level of free endogenous glutamate may be rate limiting for the glutamate-pyruvate transaminase system.

Paper Chromatographic Study On The Amino Acids Of Some Parasitic Helminths

1) Unidimensional and two dimensional paper choromatogram were prepared of 10 kinds of parastic helminths. 2) Fourteen amino acids were identified from the acid hydrolysed tissue proteins of A. lumbricoides(cuticle and musculature), A. galli, F. hepatica, E. pancreaticum, P. cervi, T. solium, and M. expansa. They were glycine, alanine, serine, threonine, methione, valine, leucine, aspartic acid, lysine, arginine, tyrosine, proline and histidine. In hydrolysates of A. lumbricoides(female genital organ) and C. sinensis, 13 amino acids were recovered. Twelve amino acid from A. lumbricoides(intestinal tract), 9 from P. westermani, and 6 from H. nana were also identified in the tissue hydrolysates.