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Guo J, Zheng W, Wang Y, Li Y, Lu S, Feng X. Coexistence of sense and anti-sense mRNAs of variant surface protein in Giardia lamblia trophozoites. Biochem Biophys Res Commun 2014; 444:439-44. [PMID: 24472547 DOI: 10.1016/j.bbrc.2014.01.074] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2014] [Accepted: 01/20/2014] [Indexed: 12/26/2022]
Abstract
A strategy of the parasitic protozoan Giardia lamblia to evade attack from the host immune system is periodic changes of its surface antigen, a member of the variant surface protein (VSP) family. A post-transcriptional gene silencing mechanism has been proposed to explain the presence of only one among many possible VSPs at any time. To investigate this phenomenon further, we extracted total RNA from cultured trophozoites of the G. lamblia C2 isolate, and cDNA was reverse-transcribed from the RNA. Sense and anti-sense VSPs were amplified from the total cDNA using nested PCR with primers designed from the 3'-conserved region and the known 5' or 3' end of the cDNA library. Sequence analyses of the amplified products revealed more than 34 full-length antisense VSPs and a smear of sense VSPs. Sequence alignments and comparisons revealed that these VSPs contained variable N-termini and conserved C-termini, and could be classified into 5 clades based on the sizes and variations of the N-terminal sequence. All antisense VSPs existed in the sense forms, but no corresponding antisense VSP existed for sense RNA (snsRNA) 16. The coexistence of sense and antisense VSP mRNAs in cultured G. lamblia supports the post-transcriptional regulation of VSP expression. We propose that VSPs transcribed simultaneously in the sense and antisense forms form double-stranded RNAs (dsRNAs) which are degraded by the Dicer endonuclease, while a VSP without an antisense transcription (e.g., snsRNA16) will be expressed on the surface of Giardia. In addition, in the course of this investigation VSPs were identified that were previously not known. PCR-based amplification of specific sense and antisense VSP cDNAs can be used to identify the specific VSP on G. lamblia trophozoites, which is easier than using specific monoclonal antibody approaches.
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Affiliation(s)
- Junli Guo
- School of Laboratory Medicine, Jilin Medical College, Jilin, Jilin 132013, China; Hainan Provincial Key Laboratory of Tropical Medicine, Hainan Medical College, Haikou 571199, China
| | - Wenyu Zheng
- Department of Hand Microsurgery, Central Hospital of Jilin City, Jilin, Jilin 132000, China
| | - Yuehua Wang
- School of Laboratory Medicine, Jilin Medical College, Jilin, Jilin 132013, China
| | - Yao Li
- School of Laboratory Medicine, Jilin Medical College, Jilin, Jilin 132013, China
| | - Siqi Lu
- Department of Parasitology, Capital Medical University, Beijing 100069, China
| | - Xianmin Feng
- School of Laboratory Medicine, Jilin Medical College, Jilin, Jilin 132013, China.
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Affiliation(s)
- César G. Prucca
- Laboratory of Biochemistry and Molecular Biology, School of Medicine, Catholic University of Cordoba, CP X5004ASK Cordoba, Argentina;
| | - Fernando D. Rivero
- Laboratory of Biochemistry and Molecular Biology, School of Medicine, Catholic University of Cordoba, CP X5004ASK Cordoba, Argentina;
| | - Hugo D. Luján
- Laboratory of Biochemistry and Molecular Biology, School of Medicine, Catholic University of Cordoba, CP X5004ASK Cordoba, Argentina;
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Hanrahan O, Webb H, O'Byrne R, Brabazon E, Treumann A, Sunter JD, Carrington M, Voorheis HP. The glycosylphosphatidylinositol-PLC in Trypanosoma brucei forms a linear array on the exterior of the flagellar membrane before and after activation. PLoS Pathog 2009; 5:e1000468. [PMID: 19503825 PMCID: PMC2685982 DOI: 10.1371/journal.ppat.1000468] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Accepted: 05/11/2009] [Indexed: 11/30/2022] Open
Abstract
Bloodstream forms of Trypanosoma brucei contain a glycosylphosphatidylinositol-specific phospholipase C (GPI-PLC) that cleaves the GPI-anchor of the variable surface glycoprotein (VSG). Its location in trypanosomes has been controversial. Here, using confocal microscopy and surface labelling techniques, we show that the GPI-PLC is located exclusively in a linear array on the outside of the flagellar membrane, close to the flagellar attachment zone, but does not co-localize with the flagellar attachment zone protein, FAZ1. Consequently, the GPI-PLC and the VSG occupy the same plasma membrane leaflet, which resolves the topological problem associated with the cleavage reaction if the VSG and the GPI-PLC were on opposite sides of the membrane. The exterior location requires the enzyme to be tightly regulated to prevent VSG release under basal conditions. During stimulated VSG release in intact cells, the GPI-PLC did not change location, suggesting that the release mechanism involves lateral diffusion of the VSG in the plane of the membrane to the fixed position of the GPI-PLC. African trypanosomes cause sleeping sickness, for which current therapy is inadequate. The parasite protects its surface from the host immune system by regularly switching its surface coat. The glycosylphosphatidylinositol-PLC only occurs in the bloodstream form, where it removes the surface coat after it enters the tsetse fly vector. Activation of the enzyme in the bloodstream would be fatal for the parasite and it is, therefore, a potential drug target. However, therapeutic strategies have been hampered by confusion over the location of the GPI-PLC despite great effort by many labs. We have used a wide variety of techniques, including one completely novel method, that exploits the dependence of detection for partially buried surface proteins on the temperature of fixation, to identify the location of the GPI-PLC in relation to other markers unequivocally. All approaches consistently show that the GPI-PLC is located exclusively in the outer leaflet of the plasma membrane covering the flagellum, where it is confined to a narrow linear array adjacent to the flagellar attachment zone. Our data have resolved the question of how enzyme and substrate meet and also suggest that chemotherapeutic agents would be able to target the GPI-PLC in its exterior location.
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Affiliation(s)
- Orla Hanrahan
- School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland
| | - Helena Webb
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Robert O'Byrne
- School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland
| | - Elaine Brabazon
- School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland
| | | | - Jack D. Sunter
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Mark Carrington
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - H. Paul Voorheis
- School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland
- * E-mail:
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Down JA, Garman SC, Gurnett AM, Turner MJ, Wiley DC. Crystallization and preliminary X-ray analysis of an intact soluble-form variant surface glycoprotein from the African trypanosome, Trypanosoma brucei. J Mol Biol 1991; 218:679-83. [PMID: 2023242 DOI: 10.1016/0022-2836(91)90254-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The intact variant surface glycoprotein (VSG) ILTat 1.24 from Trypanosoma brucei has been crystallized. An amino-terminal domain of the protein comprising two thirds of the sequence had been crystallized previously after proteolytic digestion. Now intact VSG crystals have been grown from 50 mM-Mes (pH 6.5) containing 62% (w/v) saturated ammonium sulfate. The crystals are demonstrated to contain the intact VSG by h.p.l.c. gel filtration and reaction with an antibody to the inositol phosphate oligosaccharide on the VSG carboxy terminus. The space group of the crystals is P6(2)22 (or P6(4)22) with unit cell dimensions a = b = 184 A and c = 214 A. Preparative isoelectric focusing may have facilitated crystallization.
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Affiliation(s)
- J A Down
- Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, MA 02138
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Boutignon F, Huet-Duvillier G, Mendonca-Previato L, Gomes V, Hublart M, Degand P. Variant surface glycoprotein of Trypanosoma brucei brucei AnTat 1.1: influence of the isolation conditions upon the disulfide linked dimer/monomer ratio. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. B, COMPARATIVE BIOCHEMISTRY 1990; 95:281-6. [PMID: 2328568 DOI: 10.1016/0305-0491(90)90077-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
1. Using the variant surface glycoprotein (VSG) isolation procedure described by Baltz et al. ([1976] Ann. Immunol. (Inst. Pasteur) 127 C, 761-774) which involves suspension of the trypanosomes in a pH 5.5 buffer, the Antwerpen trypanozoon antigenic type (AnTat) 1.1 VSG is mainly obtained as a disulfide linked dimeric form with a trace amount of a monomeric form. 2. The use of a parasite suspension buffer at pH 7.0 results in a slight decrease of the VSG dimer/monomer ratio. 3. pH 5.5 and 7.0 supernatants of centrifuged parasite suspensions were submitted to kinetic incubations at different temperatures and pH, and we found conditions involving transformation of the AnTat 1.1 VSG dimer into the AnTat 1.1 VSG monomer (shifting the pH 5.5 supernatant to pH 7.0 and incubation at room temperature). 4. This transformation of the AnTat 1.1 VSG dimer into the AnTat 1.1 VSG monomer is activated by the addition of 1 mM reduced glutathione, and is inhibited by the addition of 1 mM oxidized glutathione or 0.1 mM N-ethylmaleimide or cadmium acetate.
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Dagger F, Dunia I, Hernandez AG, Pradel LA, Benedetti EL. Plasma membrane and cytoskeletal constituents in Leishmania mexicana. Mol Biol Rep 1989; 13:197-206. [PMID: 2978792 DOI: 10.1007/bf00788171] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The presence and the localization of actin, spectrin and ankyrin are studied by immunofluorescence and immunoblotting in Leishmania mexicana promastigotes growing in vitro. These proteins, amphitropic in nature, coexist both in soluble and insoluble forms. Our results demonstrate that the Triton insoluble form of these proteins constitutes beside tubulin the cytoskeletal scaffold of promastigotes in close association with the plasma membrane, the axoneme and the basal body of the parasite.
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Affiliation(s)
- F Dagger
- Department of Cell Biology, Faculty of Sciences, Universidad Central de Venezuela, Caracas
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Seed JR, Sechelski JB. Immune response to minor variant antigen types (VATs) in a mixed VAT infection of the African trypanosomes. Parasite Immunol 1988; 10:569-79. [PMID: 3143096 DOI: 10.1111/j.1365-3024.1988.tb00244.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
It has been shown that soon after the onset of acute infection with Trypanosoma brucei gambiense, mice are able to detect immunologically small numbers of minor variant antigen types (VATs) within the population. However, in more longstanding infections, considerably larger populations of minor VATs are required to stimulate an effective immune response. As a result, larger populations of minor VATs evade immune detection and, following a decrease in parasitaemia, become part of the relapse population. We hypothesize that the development of immunosuppression increases the effectiveness of antigenic variation as an escape mechanism.
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Affiliation(s)
- J R Seed
- Department of Parasitology and Laboratory Practice, School of Public Health, University of North Carolina, Chapel Hill 27514
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Webster P, Grab DJ. Intracellular colocalization of variant surface glycoprotein and transferrin-gold in Trypanosoma brucei. J Cell Biol 1988; 106:279-88. [PMID: 2448312 PMCID: PMC2114974 DOI: 10.1083/jcb.106.2.279] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Endocytosis and intracellular transport has been studied in the bloodstream forms of Trypanosoma brucei by light and electron microscopy, using colloidal gold coupled to bovine transferrin (transferrin-gold). The endocytosed transferrin-gold, visualized by silver intensification for light microscopy, was present in vesicular structures between the cell nucleus and flagellar pocket of the organism. At the ultrastructural level, transferrin-gold was present after a 10-min incubation in the flagellar pocket, coated vesicles, cisternal networks, and lysosomelike structures. Endocytosis and intracellular processing of T. brucei variable surface glycoprotein (VSG) was studied using two preparations of affinity-purified rabbit IgG directed against different parts of the VSG. One preparation of IgG was directed against the cross-reacting determinant (CRD): a complex glycolipid side chain covalently linked to the COOH-terminus of the VSG molecule. The other was directed against determinants on the rest of the VSG molecule. When the two IgG preparations were used on thawed, thin cryosections of trypanosomes that had been incubated in transferrin-gold before fixation, the organelles involved with transferrin-gold endocytosis labeled with both antibodies, as well as many vesicular, tubular, and vacuolar structures that did not contain endocytosed transferrin-gold. Both antibodies also labeled the cell surface. In double-labeling experiments both antibodies were closely associated except that IgG directed against the VSG molecule labeled all the cisternae of the Golgi apparatus, whereas anti-CRD IgG was shown to label only half of the Golgi apparatus. Evidence for sorting of VSG molecules from endocytosed transferrin-gold was found. Double-labeling experiments also showed some tubular profiles which labeled on one side with anti-CRD IgG and on the other side with anti-VSG IgG, suggesting a possible segregation of parts of the VSG molecule.
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Affiliation(s)
- P Webster
- International Laboratory for Research on Animal Diseases, Nairobi, Kenya
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Pinder M, Bauer J, Fumoux F, Roelants GE. Trypanosoma congolense: lack of correlation between the resistance of cattle subjected to experimental cyclic infection or to field challenge. Exp Parasitol 1987; 64:410-7. [PMID: 3678447 DOI: 10.1016/0014-4894(87)90054-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Twelve male cattle of the Baoulé breed were exposed to natural trypanosome challenge in an area of high Glossina density, to characterize them as trypanoresistant or trypanosensitive. Weekly blood samples were taken for the determination of parasitemia and packed cell volume, as a measure of anemia. Seven Zebu cattle were also exposed to challenge at the same time. The Zebu proved to be trypanosensitive with high parasitemia, pronounced anemia and died or were drug treated in extremis. Five Baoulé were as sensitive as the Zebu while 7 others were trypanoresistant since they showed little or no patent parasitemia, only mild transient anemia and survived in good condition. The 12 Baoulé were allowed to recover from challenge in the field and along with 7 Zebu were subjected to experimental fly challenge in fly-proof accommodation. Glossina morsitans submorsitans infected with a clone of Trypanosoma congolense derived from the stock Serengeti/71/STIB/212 were allowed to engorge on the shaven flanks of tranquilized animals. All animals showed persistent parasitemia for at least 7 weeks, including all the Baoulé resistant to natural challenge. Two Baoulé, one resistant and one sensitive to natural challenge, and 4/7 Zebu appeared unable to control parasitemia, had severe anemia, and were drug treated in extremis. The remaining Baoulé, 6 resistant and 4 sensitive, appeared to be undergoing spontaneous cure by Week 9-10, as did 3/7 Zebu. In Zebu, anemia was as pronounced as under natural challenge. Three resistant Baoulé maintained packed cell volume above 30 as under field challenge but the others showed marked anemia. On the contrary, 4 sensitive Baoulé showed only slight anemia after artificial fly challenge.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Pinder
- Centre de Recherches sur les Trypanosomoses Animales (CRTA), Burkina Faso, West Africa
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10
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Lamont GS, Fox JA, Cross GA. Glycosyl-sn-1,2-dimyristylphosphatidylinositol is the membrane anchor for Trypanosoma equiperdum and T. (Nannomonas) congolense variant surface glycoproteins. Mol Biochem Parasitol 1987; 24:131-6. [PMID: 2957588 DOI: 10.1016/0166-6851(87)90099-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
We have analysed the structures of the Trypanosoma (Nannomonas) congolense and T. equiperdum variant surface glycoprotein (VSG) membrane anchors. Myristic acid uptake, phospholipase treatment, and nitrous acid deamination showed that, for each species, the anchor is glycosyl-sn-1,2-dimyristylphosphatidylinositol, as has been previously described for T. brucei. Osmotic lysis of these trypanosomes resulted in the release of soluble VSG, lacking fatty acid. In both species and in T. evansi, an endogenous phospholipase C, which cleaved diacylglycerol from membrane form VSG, was identified.
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11
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Affiliation(s)
- M G Low
- Oklahoma Medical Research Foundation, Oklahoma City 73104
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12
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Jones R, Brown CR. Identification and characterization of the 2D6 and Mr 23,000 antigens on the plasma membrane of rat spermatozoa. Biochem J 1987; 241:353-60. [PMID: 2439064 PMCID: PMC1147568 DOI: 10.1042/bj2410353] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Previous investigations [Jones, Brown, von Glos & Gaunt (1985) Exp. Cell Res. 156, 31-44] have demonstrated the appearance of a new antigenic determinant (recognized by monoclonal antibody 2D6) on the plasma membrane of rat spermatozoa during post-testicular maturation in the epididymis. Identification of the 2D6 antigen on Western blots from one-dimensional SDS/polyacrylamide gels revealed that it co-migrated with a membrane protein (designated Mr 23,000 antigen) present on testicular and immature germ cells, suggesting that one antigen might be a modified version of the other. In the present work, however, we demonstrate that, although they have similar Mr and are present in soluble and membrane-bound forms, the 2D6 and Mr 23,000 antigens are biochemically and immunologically distinct molecules. The properties of the antigens are described and compared. The Mr 23,000 antigen is present on both testicular and cauda epididymidal spermatozoa, has a pI of 6.1, contains no detectable carbohydrate, is not tissue-specific and is degraded by V8 protease. By contrast, the 2D6 antigen is glycosylated, has a broad pI from 4.5 to 6.1, is tissue- and species-specific and is resistant to digestion with V8 protease. Its role in sperm-egg recognition is discussed.
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Metcalf P, Blum M, Freymann D, Turner M, Wiley DC. Two variant surface glycoproteins of Trypanosoma brucei of different sequence classes have similar 6 A resolution X-ray structures. Nature 1987; 325:84-6. [PMID: 2432433 DOI: 10.1038/325084a0] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Antigenic variation in the African trypanosome is mediated through changes in the composition of the surface coat. By controlling expression of the major surface protein, the variant surface glycoprotein (VSG), from a repertoire of perhaps 1,000 different genes the organisms exhibit a series of antigenically distinct coats and evade the host's immune system. We have determined the 6 A resolution structure of a T. brucei variant surface glycoprotein, ILTat 1.24, using X-ray crystallography. The crystallized protein consists of the N-terminal two-thirds of the intact VSG which has a relative molecular mass (Mr) of 60,000 (60K). The structure, which includes a 90 A long alpha-helical bundle, is strikingly similar to that of the N-terminal fragment of VSG MITat 1.2 (ref. 4). Although most known VSG sequences show little similarity of primary sequence in the N-terminal domain, the similarity between the structure of a Class I (ILTat 1.24) and a Class II (MITat 1.2) VSG antigen suggests that VSGs may share a common tertiary structure.
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14
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Hereld D, Krakow JL, Bangs JD, Hart GW, Englund PT. A phospholipase C from Trypanosoma brucei which selectively cleaves the glycolipid on the variant surface glycoprotein. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(18)67092-9] [Citation(s) in RCA: 88] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Bordier C, Etges RJ, Ward J, Turner MJ, Cardoso de Almeida ML. Leishmania and Trypanosoma surface glycoproteins have a common glycophospholipid membrane anchor. Proc Natl Acad Sci U S A 1986; 83:5988-91. [PMID: 3461472 PMCID: PMC386422 DOI: 10.1073/pnas.83.16.5988] [Citation(s) in RCA: 91] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The variant surface glycoprotein (VSG) of the African trypanosomes is the major membrane protein of the plasma membrane of the bloodstream stage of the parasite. It is anchored in the plasma membrane by a glycolipid covalently bound to the C-terminal amino acid of the protein. The VSG is released through the action of a phosphatidylinositol-specific phospholipase C that removes dimyristoylglycerol and exposes the carbohydrate antigenic determinant common to all VSGs. Promastigotes of Leishmania have a predominant surface glycoprotein, termed p63, that is anchored in the plasma membrane in a similar way. A water-soluble form of p63 can be generated through the action of phosphatidylinositol-specific phospholipase C from trypanosomes or from Bacillus cereus. Either treatment exposes on the Leishmania p63 an antigenic determinant recognized by antibody prepared against the trypanosomal crossreacting determinant. These findings indicate that p63 and VSG have a common membrane anchor and are structurally related.
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Bangs JD, Andrews NW, Hart GW, Englund PT. Posttranslational modification and intracellular transport of a trypanosome variant surface glycoprotein. J Cell Biol 1986; 103:255-63. [PMID: 3722267 PMCID: PMC2113794 DOI: 10.1083/jcb.103.1.255] [Citation(s) in RCA: 132] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
After synthesis on membrane-bound ribosomes, the variant surface glycoprotein (VSG) of Trypanosoma brucei is modified by: (a) removal of an N-terminal signal sequence, (b) addition of N-linked oligosaccharides, and (c) replacement of a C-terminal hydrophobic peptide with a complex glycolipid that serves as a membrane anchor. Based on pulse-chase experiments with the variant ILTat-1.3, we now report the kinetics of three subsequent processing reactions. These are: (a) conversion of newly synthesized 56/58-kD polypeptides to mature 59-kD VSG, (b) transport to the cell surface, and (c) transport to a site where VSG is susceptible to endogenous membrane-bound phospholipase C. We found that the t 1/2 of all three of these processes is approximately 15 min. The comparable kinetics of these processes is compatible with the hypotheses that transport of VSG from the site of maturation to the cell surface is rapid and that VSG may not reach a phospholipase C-containing membrane until it arrives on the cell surface. Neither tunicamycin nor monensin blocks transport of VSG, but monensin completely inhibits conversion of 58-kD VSG to the mature 59-kD form. In the presence of tunicamycin, VSG is synthesized as a 54-kD polypeptide that is subsequently processed to a form with a slightly higher Mr. This tunicamycin-resistant processing suggests that modifications unrelated to N-linked oligosaccharides occur. Surprisingly, the rate of VSG transport is reduced, but not abolished, by dropping the chase temperature to as low as 10 degrees C.
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18
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Gurnett AM, Ward J, Raper J, Turner MJ. Purification and characterisation of membrane-form variant surface glycoproteins of Trypanosoma brucei. Mol Biochem Parasitol 1986; 20:1-13. [PMID: 3016534 DOI: 10.1016/0166-6851(86)90137-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Membrane-form variant surface glycoprotein of Trypanosoma brucei can be prepared in the presence of para-chloromercuriphenylsulphonic acid. The membrane-bound enzyme that usually cleaves a lipid from this glycoprotein, thus producing the soluble variant surface glycoprotein, is inhibited by a range of sulphydryl reagents. The effect of such inhibitors, both on cell lysates and on semi-purified enzyme, reveals that the enzyme may have a sulphydryl at or near its active site. Fatty acid analysis and isoelectric point measurements of membrane form and soluble form are presented.
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Devine DV, Falk RJ, Balber AE. Restriction of the alternative pathway of human complement by intact Trypanosoma brucei subsp. gambiense. Infect Immun 1986; 52:223-9. [PMID: 3633873 PMCID: PMC262223 DOI: 10.1128/iai.52.1.223-229.1986] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
We studied the interaction of African trypanosomes with human complement. Bloodstream forms of Trypanosoma brucei subsp. gambiense isolated from mice activated the alternative pathway of complement during a 30-min incubation in vitro. In human serum, all cells remained intact and motile during this period. C3 was detected on the surface by a direct binding assay with a monoclonal antibody which recognizes C3b and iC3b. C3 deposition could also be detected by this radioimmunoassay when parasites were incubated with purified C3. Such C3 binding was enhanced by factor B, factor D, and magnesium. Surface deposition of factor B was demonstrated both by flow immunofluorescence analysis and binding of radiolabeled factor B. C3 binding and factor B binding were inhibitable by EDTA but not by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N' -tetraacetic acid (EGTA). The inhibited binding could be restored by addition of magnesium. No human immunoglobulin G or mouse immunoglobulin was detected on the trypanosome surface. By flow cytometry, neither human C5 nor polymerized C9 was detected on trypanosomes incubated in serum, although this assay was able to detect C5 and C9 on the surface of complement-treated human erythrocytes. Using a radioimmunoassay which measures C5b-9 in serum, we found that there was no generation of SC5b-9 in serum which had been incubated with trypanosomes. We concluded that, although trypanosomes activate the alternative pathway of complement, they are not lysed, because the cascade does not continue beyond the establishment of C3 convertase.
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Abstract
Previously quoted figures for the frequency of antigen switching in Trypanosoma brucei are based on incorrect assumptions. In order to determine the correct switching frequency, an equation was derived that takes the growth rates of the newly expressed antigen types into consideration as well as the proportion of switched trypanosomes and the number of generations since the population was antigenically homogeneous. When this equation was applied to published in vitro data, variable values were obtained for the switching frequency in clonal populations originally expressing one antigen type. The calculated most likely switching frequencies ranged from 1.4 X 10(-7) to 3.5 X 10(-6). This variation was probably caused by differences in the growth rates of the new antigen types in the population and failure to detect slow growing variants. To overcome these problems, an experimental procedure was developed to analyse the switching frequency in vitro. Trypanosomes were cloned and grown in parallel cultures. After an appropriate number of generations, cells expressing the original antigen type were destroyed and, from the proportion of cultures that contained new antigen types, the switching frequency was calculated. The technique minimized subculturing or other procedures that could distort the results. Although the method was optimized for analysing switching frequency, the values differed between experiments, ranging from 2.2 X 10(-7) to 2.6 X 10(-6) for one variant. Possible causes for the variations in switching frequency are discussed.
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Antigenic variation during Trypanosoma vivax infections of different host species. Parasitology 1986; 92 ( Pt 1):51-65. [PMID: 2421230 DOI: 10.1017/s0031182000063447] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The sequence of appearance of specific lytic activity against more than 20 variable antigen types (VATs) of Trypanosoma vivax in the serum of 27 animals belonging to 5 species has been examined. For each host species there was a characteristic course of infection, with differences in height and duration of parasitaemia and in pathogenicity. The sequence of antigenic variation was similar in all host species, with some VATs consistently eliciting response more rapidly than others. The predominant group, comprising VATs which apparently developed within the first 3 weeks, varied in size according to the total number of trypanosomes in the bloodstream within that period, suggesting there is a spectrum, rather than discrete groupings, in the hierarchy of VAT expression. There was very little evidence for differences in appearance of VATs between host species; the only clear example was one VAT which apparently did not develop in one host species. The sequence of antigenic variation in T. vivax seems to be determined by the parasite rather than the host species.
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Gurnett AM, Raper J, Turner MJ. Solution properties of the variant surface glycoprotein of Trypanosoma brucei. Mol Biochem Parasitol 1986; 18:141-53. [PMID: 3960052 DOI: 10.1016/0166-6851(86)90034-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The solution properties of the membrane form and soluble form of variant surface glycoproteins from Trypanosoma brucei have been compared. Solution cross-linking studies established that both forms are dimers, although dissociation of membrane-form variant surface glycoprotein can be promoted by certain ionic and zwitterionic detergents. Sedimentation coefficients were measured under a range of conditions, and the results were comparable with the results of solution cross-linking. Stokes radii were measured by gel filtration, allowing a value for the frictional coefficient to be calculated. The two forms show no differences other than those consistent with binding of detergent micelles to the hydrophobic moiety present on membrane form surface glycoprotein. This validates the use of soluble variant surface glycoprotein in X-ray crystallography experiments.
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Majiwa PA, Young JR, Hamers R, Matthyssens G. Minichromosomal variable surface glycoprotein genes and molecular karyotypes of Trypanosoma (Nannomonas) congolense. Gene 1986; 41:183-92. [PMID: 3710162 DOI: 10.1016/0378-1119(86)90097-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Employing orthogonal-field-alternation gel electrophoresis (OFAGE), we have separated chromosome-sized DNA molecules from Trypanosoma (Nannomonas) congolense clones, the clones being derived from several distinct antigenic repertoires. Trypanosome clones that belong to a specific antigenic repertoire appear to have a chromosome pattern characteristic of that particular repertoire. Hybridization of the separated chromosomes with cloned DNA fragments encoding variable surface glycoproteins revealed the presence of two different T.(N.) congolense variable surface glycoprotein genes on mini-chromosomes (mc) and the modes by which these genes may be activated: one by duplicative and the other by non-duplicative activation.
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Ferguson MA, Duszenko M, Lamont GS, Overath P, Cross GA. Biosynthesis of Trypanosoma brucei variant surface glycoproteins. N-glycosylation and addition of a phosphatidylinositol membrane anchor. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(17)42479-3] [Citation(s) in RCA: 149] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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Low MG, Kincade PW. Phosphatidylinositol is the membrane-anchoring domain of the Thy-1 glycoprotein. Nature 1985; 318:62-4. [PMID: 2865681 DOI: 10.1038/318062a0] [Citation(s) in RCA: 300] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Glycoproteins exposed on cell surfaces are commonly anchored in the membrane via hydrophobic peptide domains which penetrate the lipid bilayer. However, it has recently been appreciated that there are exceptions to this generalization and certain cell-surface proteins appear to be anchored via a specific association with phosphatidylinositol. Thy-1 glycoprotein may also be attached to cell membranes by a non-protein hydrophobic domain located at the C-terminus and although the chemical nature of this moiety has not been determined, it was postulated that it might be a lipid. On the other hand, amino-acid sequences predicted from nucleotide sequence analyses suggest that a C-terminal hydrophobic peptide segment not found in the purified, detergent-solubilized Thy-1 glycoprotein may be responsible for attachment. We report here that a highly purified phospholipase C specific for phosphatidylinositol selectively released Thy-1 from viable normal or malignant T lymphocytes. This result supports the proposed lipid nature of the Thy-1 anchoring domain and further suggests that this lipid is, or is closely related to, phosphatidylinositol.
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Ferguson MA, Low MG, Cross GA. Glycosyl-sn-1,2-dimyristylphosphatidylinositol is covalently linked to Trypanosoma brucei variant surface glycoprotein. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(17)38603-9] [Citation(s) in RCA: 288] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Synthesis of a hydrolase for the membrane-form variant surface glycoprotein is repressed during transformation of Trypanosoma brucei. FEBS Lett 1985; 187:105-10. [PMID: 2991000 DOI: 10.1016/0014-5793(85)81223-0] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A membrane-bound phospholipase C-like hydrolase present in lysates of bloodstream forms of Trypanosoma brucei rapidly converts the membrane form of the variant surface protein to the soluble form and 1,2-dimyristoylglycerol [(1985) M.A.J. Ferguson et al. J. Biol. Chem., 260, 4963-4968]. The hydrolase is inhibited by p-chloromercuribenzenesulfonate. The synthesis of the enzyme is rapidly repressed upon differentiation of bloodstream forms to procyclic cells and the enzyme activity declines to an undetectable level during subsequent growth of procyclic forms.
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Ferguson MA, Haldar K, Cross GA. Trypanosoma brucei variant surface glycoprotein has a sn-1,2-dimyristyl glycerol membrane anchor at its COOH terminus. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)89166-9] [Citation(s) in RCA: 112] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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29
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Turner MJ. Structure and variation within variant surface glycoproteins of Trypanosoma brucei. ANNALES DE L'INSTITUT PASTEUR. IMMUNOLOGIE 1985; 136C:41-9. [PMID: 3994303 DOI: 10.1016/s0769-2625(85)80038-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Variant surface glycoproteins of the African trypanosomes are members of a multigene family which show extraordinary amino sequence diversity. The extent of this diversity and the significance of homologies both in the amino acid sequence and in the post-translational modifications are discussed in the light of what is predicted for the structure of these molecules and what is now known from X-ray crystallographic analysis.
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