The surface of the African trypanosomes

The African trypanosomes bear on the outside of their cell membrane a single 10-15 nm thick coat of a glycoprotein. This glycoprotein may differ in structure in the predominant populations of parasitemic waves found in relapsing infections. Variant Specific Glycoprotein (VSG) range in MW between 53,000-63,000 d and may have variable amounts of carbohydrate attached at one, two, or several loci. Such differences in carbohydrate content may account in part for their range in molecular size. Approximately 30 C-terminal residues demonstrate isotypy ; i.e. these regions fall into classes having similar amino acid sequence. Modest homology has been demonstrated in two VSGs of T. congolense arising in relapsing infections although comparison of many VSG show little or no obvious homology. More recently, lipid-associated forms of VSG have been described and it is believed that these forms may be transmembrane proteins. Different VSGs appear to have different amounts of the primary sequence which have alpha-helix-forming potential. In some VSG, in excess of 80% of the structure is helical as judged by both Chou-Fasman calculations and by circular dichroism. This raises the possibility that different VSG may have different folding patterns. The arrangement of VSG on the trypanosome surface probably places the basic amino acid-rich carbohydrate-bearing C-terminus of the polypeptide chain close to the membrane. There is some protein-protein association between VSGs for which (in T. evansi) the C-terminal tail is not required. The importance of VSG structure lies not only in the fact that the molecule mediates the phenomenon of antigenic variation but also in the recent observation that VSG may act on the cellular immune system to suppress the humoral immune responses of the host.

Trypanosoma rhodesiense bloodstream trypomastigote and culture procyclic cell surface carbohydrates

Bloodstream trypomastigote and culture procyclic (insect midgut) forms of a cloned T. rhodesiense variant (WRAT at 1) were tested for agglutination with the lectins concanavalin A (Con A), phytohemagglutinin P (PP), soybean agglutinin (SBA), fucose binding protein (FBP), wheat germ agglutinin (WGA), and castor bean lectin (RCA). Fluorescence-microscopic localization of lectin binding to both formalin-fixed trypomastigotes and red cells was determined with fluorescein isothiocyanate (FITC)-conjugated Con A, SBA, FBP, WGA, RCA, PNA (peanut agglutinin), DBA (Dolichos bifloris), and UEA (Ulex europaeus) lectins. Electron microscopic localization of lectin binding sites on bloodstream trypomastigotes was accomplished by the Con A-horseradish peroxidase-diamino-benzidine (HRP-DAB) technique, and by a Con A-biotin/avidin-ferritin method. Trypomastigotes, isolated by centrifugation or filtration through DEAE-cellulose or thawed after cryopreservation, were agglutinated by the lectins Con A and PP with agglutination strength scored as Con A greater than PP. No agglutination was observed in control preparations or with the lectins WGA, FBA or SBA. Red cells were agglutinated by all the lectins tested. Formalin-fixed bloodstream trypomastigotes bound FITC-Con A and FITC-RCA but not FITC-WAG, -SBA, -PNA, -UEA or -DBA lectins. All FITC-labeled lectins bound to red cells. Con A receptors, visualized by Con A-HRP-DAB and Con A-biotin/avidin-ferritin techniques, were distributed uniformly on T. rhodesiense bloodstream forms. No lectin receptors were visualized on control preparations. Culture procyclics lacked a cell surface coat and were agglutinated by Con A and WGA but not RCA, SBA, PP and FBP. Procyclics were not agglutinated by lectins in the presence of competing sugar at 0.25 M.(ABSTRACT TRUNCATED AT 250 WORDS)

Presence of glycerol and fatty acids in the C-terminal end of a variant surface glycoprotein from Trypanosoma equiperdum

The composition of the C-terminal end of a variant surface glycoprotein from Trypanosoma equiperdum (BoTat-1 VSG) has been examined. It has been reported for two Trypanosoma brucei VSGs (Holder, A.A., Biochem. J. (1983), 209, 261-262) that ethanolamine was involved in binding the C-terminal amino acid to an oligosaccharide side chain. Tryptic glycopeptides were prepared from BoTat-1 VSG and analyzed. One of them was found to contain ethanolamine and consequently was assumed to be C-terminal. It was shown that the glycopeptide also included phosphate, glycerol and fatty acids. The fatty acid composition was representative of that of glycerolipids. All the results suggest that the end of the molecule is a core of phosphatidylethanolamine.

Differentiation of Trypanosoma cruzi Chagas, 1909 and Trypanosoma vespertilionis Battaglia, 1904 by various lectins

Four-days-old culture forms of Trypanosoma cruzi (strain Téhuantépéc, Guatemala) and Trypanosoma vespertilionis (strain P-14, P-9) were tested by 19 carbohydrate-specific agglutinins. The T. cruzi strains are interspecifically distinguishable with the lectins from Euonymus europaeus, Tridacna crocea, Tridacna maxima and the human blood-group testserum anti-B from the T. vespertilionis strains. While the T. vespertilionis strains did react with anti-B and E. europaeus, the T. cruzi strains did not agglutinate. The T. cruzi strains were agglutinated by the lectins from T. crocea and T: maxima while the bat-trypanosomes showed no reactions. Using these lectins it was not possible to distinguish the bat-flagellates intraspecifically. With the lectins from Triticum vulgaris and Arachis hypogaea the T. cruzi strains could be distinguished. While the Ténuantépéc strain did agglutinate with A. hypogaea, T. cruzi strain Guatemala did react only with the lectin from T. vulgaris. The bat-trypanosomes were agglutinated only by A. hypogaea but not by T. vulgaris. The reactions of these trypanosome-species with A. papillata and T. vulgaris demonstrate that both trypanosome species have N-acetylneuraminic acid on their cell surfaces.

Partial determination of the primary structure of a variant surface glycoprotein from Trypanosoma equiperdum. Composition and location of a carbohydrate moiety

Salivarian trypanosomes have the ability to evade the immune response of their hosts by the sequential expression of different cell surface glycoproteins. Among the isolated specific antigens from cloned variants of Trypanosoma equiperdum, a structural study was undertaken on two immunologically cross-reacting variant surface glycoproteins, and results concerning the basic antigenic type are reported. The glycoprotein was cleaved by cyanogen bromide, and amino acids of several purified fractions obtained by gel filtration chromatography of this cleavage mixture were sequenced by automated Edman degradation. Sequencing in particular allowed the identification of the N-terminal portion of the molecule (residues 1-74). Sugar compositions of the fractions have demonstrated the presence of at least two carbohydrate moieties in the glycoprotein. Using a subsequent enzymatic subcleavage we were able to locate the first glycosylation site in position 57. An important observation was that the first oligosaccharide identified was rich in mannose and devoid of galactose.

The fatty acids of Trypanosoma vivax

A study was carried out to determine the lipid composition of the blood-stream form of the African trypanosome. Trypanosoma vivax. Data from thin layer chromatography showed that the major polar lipids were lysophosphatidylcholine, sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and diphosphatidylglycerol. The major neutral lipids were sterol, monoacylglycerol, diacylglycerol, free fatty acid and triacyglycerol. 16:0, 18:0, 18:1 and 18:2 constituted the major fatty acids of both the polar and neutral lipid fractions. The work constituted the first detailed study on the fatty acid composition of this African trypanosome.

Comparative studies of Trypanosoma cruzi and T. cruzi-like stocks from different South American countries using lectins

The agglutination behaviour of four-day-old epimastigote culture forms of 34 Trypanosoma cruzi, and T. cruzi-like stocks from Brazil, Chile, Colombia, Ecuador and Peru were tested with 15 carbohydrate-specific lectins. We distinguished intraspecifically two groups of agglutination reactions: Group 1 includes stocks which react with Triticum vulgaris and Aaptos papillata II (wheat germ agglutinin: WGA-type). Group 2 includes stocks agglutinated by Arachis hypogaea and Aaptos papillata II (peanut lectin: PNA-type). The agglutination reactions with lectins from Triticum vulgaris and Aaptos papillata II correlate with the presence of N-acetylneuraminic acid on the cell surface. After treatment with neuraminidase, the WGA-type is agglutinated by PNA but not by lectins from Triticum vulgaris and Aaptos papillata II. Further results demonstrate that a certain zymodeme pattern can be correlated with carbohydrate determinants.

Electrophoretic analysis of endonuclease-generated fragments of k-DNA, of esterase isoenzymes, and of surface proteins as aids for species identification of insect trypanosomatids

In order to verify the applicability of biochemical methods for species identification of Trypanosomatidae, 13 species of monoxenic trypanosomatids plus the heteroxenous Trypanosoma cruzi were comparatively analyzed by three different biochemical methods. Insect trypanosomatids examined were: Crithidia acanthocephali, C. fasciculata (three varieties), C. luciliae luciliae, C. luciliae thermophila, C. deanei, C. oncopelti, Herpetomonas muscarum muscarum, H. megaseliae, H. samuelpessoai, H. mariadeanei, Leptomonas seymouri, L. collosoma, L. samueli, and Blastocrithidia culicis. Also included in the survey were aposymbiotic strains of C. deanei and C. oncopelti. Methods used were: electrophoretic profiling of endonuclease-generated fragments of k-DNA, esterase isoenzymes profiling, and polyacrylamide-gel electrophoresis (SDS-PAGE) of radioiodinated cell surface proteins. Interspecific but not intraspecific differences were detected by all three methods among the 13 monoxenic species examined. Thus, it is concluded that these methods can be successfully used, in addition to classical criteria, for species identification of insect trypanosomatids.

The variable surface glycoproteins of Trypanosoma equiperdum are phosphorylated

The phosphoproteins from three Trypanosoma equiperdum variants were studied by labelling the parasites in vivo with 32P. Phosphoprotein analysis reveals the presence of a 58 000 mol. wt. phosphoprotein ( pp58 ) which is absent when live trypanosomes are pre-treated with proteinase K under conditions where only the surface coat containing the variable surface glycoprotein (VSG) is removed. Immunological and fingerprint analysis on labelled pp58 , purified from these variants by affinity chromatography on Concanavalin A-Sepharose, clearly identify this component as the VSG. Furthermore, the VSGs seem to be phosphorylated to the extent of 1 mol phosphate per mol glycoprotein. The phosphorylated region is located in the extreme C-terminal region representing approximately 10% of the total molecule. The phosphorylated residue is not an aliphatic or aromatic ester of serine, threonine, or tyrosine, nor an acyl phosphate involving an aspartyl or glutamyl residue, nor phosphohistidine. The evidence that VSGs are phosphorylated could have considerable implications for the transfer and function of these structures.

The 5S ribosomal RNA of Euglena gracilis cytoplasmic ribosomes is closely homologous to the 5S RNA of the trypanosomatid protozoa

The complete nucleotide sequence of the major species of cytoplasmic 5S ribosomal RNA of Euglena gracilis has been determined. The sequence is: 5' GGCGUACGGCCAUACUACCGGGAAUACACCUGAACCCGUUCGAUUUCAGAAGUUAAGCCUGGUCAGGCCCAGUUAGUAC UGAGGUGGGCGACCACUUGGGAACACUGGGUGCUGUACGCUUOH3'. This sequence can be fitted to the secondary structural models recently proposed for eukaryotic 5S ribosomal RNAs (1,2). Several properties of the Euglena 5S RNA reveal a close phylogenetic relationship between this organism and the protozoa. Large stretches of nucleotide sequences in predominantly single-stranded regions of the RNA are homologous to that of the trypanosomatid protozoan Crithidia fasticulata. There is less homology when compared to the RNAs of the green alga Chlorella or to the RNAs of the higher plants. The sequence AGAAC near position 40 that is common to plant 5S RNAs is CGAUU in both Euglena and Crithidia. The Euglena 5S RNA has secondary structural features at positions 79-99 similar to that of the protozoa and different from that of the plants. The conclusions drawn from comparative studies of cytochrome c structures which indicate a close phylogenetic relatedness between Euglena and the trypanosomatid protozoa are supported by the comparative data with 5S ribosomal RNAs.

Sialic acids are responsible for charge heterogeneity of the variant surface glycoprotein of Trypanosoma congolense

Intact living cells of Trypanosoma congolense can be labeled by periodate/borotritide. The procedure described introduces a radioactive label nearly exclusively into the variant surface glycoprotein (VSG). The label can be removed from the VSG by either neuraminidase treatment or by mild acid hydrolysis. Using thin-layer chromatography the labeled compounds comigrated with 5-acetamido [or 5-glycolamide]3,5-dideoxygalactooctulosonic acid and 5-acetamido [or 5-glycolamide]3,5-dideoxyarabinoheptulosonic acid. These are the compounds commonly obtained after periodate borotritide treatment of glycosidically-linked neuraminic acids. It is evident from the results that sialic acids are constituents of the carbohydrate moieties of the VSG of T. congolense. Sialic acids are responsible for the charge heterogeneity of the VSG which is observed after isoelectric focusing.

Kinetoplast DNA in Trypanosoma equinum

Identification and characterization of kDNA is described in the naturally occurring totally dyskinetoplastic species Trypanosoma equinum. Fluorescence microscopy of live cells, using the highly sensitive and specific probe DAPI (4,6-diamidino-2-phenyl-indole), showed the presence of a diversity of extranuclear fluorescent bodies scattered along the length of the organism. Transmission electron microscopic studies revealed a close similarity between the distribution of these DAPI-fluorescing particles and of dense aggregates of nonfibrillar material resembling the kDNA of dyskinetoplastic strains of other species. Variable sized remnants of kDNA, occurring singly or in clusters, were found scattered throughout the mitochondrion. Analytical cesium chloride ultracentrifugation of total cellular DNA extracts showed a kDNA banding profile at a buoyant density equal to 1.691 gm/cm3, representing approximately 11% of the total cellular DNA content. Molecular spreads of isolated kDNA revealed a population of open circular molecules ranging in contour length from 0.11-9.69 micrometer.

The kinetoplast DNA of Trypanosoma equiperdum

We have analyzed the kinetoplast DNA for Trypanosoma equiperdum (American Type Culture Collection 30019) and two dyskinetoplastic strains derived from it. The DNA networks from the kinetoplastic strain are made up of catenated mini-circles and maxi-circles, like the networks from the closely-related Trypanosoma brucei. The mini-circles of T. equiperdum lack the pronounced sequence heterogeneity of T. brucei mini-circles, as shown by the fragment distribution of restriction digests and by the predominance of well-matched duplexes in electron micrographs of renatured DNA. The electrophoretic analysis of kinetoplast DNA digested with various restriction endonucleases shows the maxi-circle of T. equiperdum to consist of circular DNA molecules of 8.4 x 10(6) daltons, without size or sequence heterogeneity or repetitious segments. A comparison of the sequence by restriction endonuclease fragmentation and hybridization shows extensive sequence homology. The size difference between both maxi-circles is due to the deletion of one continuous segment of 5.10(6) daltons. In the two dyskinetoplastic strains, we cannot detect DNA sequences that hybridize with kinetoplast DNA from T. brucei or from the kinetoplastic strain of T. equiperdum. In one of these strains, a 'low-density' DNA fraction contained a simple sequence DNA, cleaved by restriction endonuclease HindIII into fragments of 180 base-pairs and multimers of this. The relation of this DNA to kinetoplast DNA, if any, is unknown.

Absence of kinetoplast DNA in a late antigenic variant of Trypanosoma equiperdum

We have analysed by several biochemical techniques the DNA components of two antigenic variants isolated from Trypanosoma equiperdum. We did not observe any kinetoplast DNA (kDNA) structures or networks in the late antigen variant BoTat 28. Furthermore, the results of reassociation kinetics of in vitro labelled kDNA show that neither kDNA minicircle sequences nor kDNA maxicircle sequences of BoTat 1, the basic antigen type, can be detected in the total DNA of BoTat 28.

Evidence for concanavalin A binding sites on the surface coat of Trypanosoma congolense

Glycoproteins of Trypanosoma congolense have been detected on SDS-polyacrylamide gels using the Concanavalin A peroxidase technique. Using [35S]diazoniobenzenesulphonate as a marker for cell surface proteins it was possible to distinguish between internal glycoproteins and the surface coat proteins. On SDS-polyacrylamide gels Con A reacted with the surface coat proteins. Results obtained from Con A-induced agglutination of living trypanosomes indicated that sugars of the surface coat proteins were accessible to Con A. This was reinforced by the cytochemical visualization of Con A binding to the trypanosome surface. The results suggested that the surface coat protein contained alpha-linked D-mannosyl, D-glucosyl, or N-acetyl-D-glucosaminoyl residues, which are exposed exteriorly on the surface coat.

Characterization of the molecular components in kinetoplast-mitochondrial DNA of Trypanosoma equiperdum. Comparative study of the dyskinetoplastic and wild strains

The structure of the kinetoplast DNA of Trypanosoma equiperdum has been studied and compared to the structure of the circular mitochondrial DNA extracted from a dyskinetoplastic strain of T. equiperdum. In T. equiperdum wild type, the kinetoplast DNA constitutes approximately 6% of the total cellular DNA and is composed of approximately 3,000 supercoiled minicircles of 6.4 x 10(5) daltons and approximately 50 circular supercoiled molecules of 15.4 x 10(6) daltons topologically interlocked; The buoyant density in CsCl of the minicircles is 1.691 g/cm 3. The large circles have a buoyant density of 1.684 g/cm 3, are homogeneous in size and are selectively cleaved by several restriction endonucleases which do not cleave the minicircles. The cleavage sites of six different restriction endonucleases have been mapped on the large circle. The minicircles are cleaved by two other restriction endonucleases, and their cleavage sites have been mapped. The mitochondrial DNA extracted from the dyskinetoplastic strain of T. equiperdum represents 7% of the total DNA of the cell and is composed of supercoiled circles, heterogeneous in size, and topologically associated in catenated oligomers. Its buoyant density in CsCl is 1.688 g/cm 3. These molecules are not cleaved by any of the eight restriction endonucleases tested. The reassociation kinetics of in vitro labeled kDNA minicircles and large circles has been studied. The results indicate that the minicircles as well as the large circles are homogeneous in sequence and that the circular DNA of the dyskinetoplastic strain has no sequence in common with the kDNA of the wild strain.

Dyskinetoplasty in two species of trypanosomatids

Dyskinetoplastic cells from both Crithidia fasciculata and Trypanosoma equiperdum lack detectable kinetoplast DNA (kDNA) by conventional staining techniques. Two dyskinetoplastic strains of T. equiperdum, either acriflavine-induced or spontaneously occurring, show normal amounts of kDNA (p = 1.692 g/cm3) in analytical caesium chloride, ultracentrifugation. Electron and fluorescence microscopy of the dyskinetoplastic strains of T. equiperdum suggest that the kDNA network is fragmented and dispersed throughout the mitochondrion. The fragmentation and dispersion of the kDNA, rather than a reduction in the amount of kDNA, is the cause of the lack of kinetoplast staining in the dyskinetoplastic strains of T. equiperdum. Acriflavine-treated cultures of C. fasciculata show a decrease in the amount of kDNA (p = 1.703 g/cm3) corresponding to the percentage of dyskinetoplastic cells in the cultures. Electron and fluorescence microscopy of acriflavine-treated cultures of C. fasciculata show the loss of the kDNA network in cells which lack Giemsa and Feulgen staining, confirming the hypothesis that the kDNA is lost in dyskinetoplastic trypanosomatids from insects. Possible modes of acriflavine action are considered and a proposed mechanism for acriflavine action in trypanosomes from mammals is presented.