scholarly journals Black-necked spitting cobra (Naja nigricollis) phospholipases A2 cause Trypanosoma brucei death by blocking endocytosis through the flagellar pocket

2021 ◽  
Author(s):  
Andrea Martos-Esteban ◽  
Olivia J. S. Macleod ◽  
Isabella Maudlin ◽  
Konstantinos Kalogeropoulos ◽  
Jonas A. Jurgensen ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Trypanosoma Brucei ◽  
Antigenic Variation ◽  
Adaptive Immune Response ◽  
Surface Glycoprotein ◽  
Covalent Attachment ◽  
Mammalian Host ◽  
Flagellar Pocket ◽  
African Trypanosomes ◽  
External Face

African trypanosomes, such as Trypanosoma brucei, are flagellated protozoa which proliferate in mammals and cause a variety of diseases in people and animals. In a mammalian host, the external face of the African trypanosome plasma membrane is covered by a densely packed coat formed of variant surface glycoprotein (VSG), which counteracts the host adaptive immune response by antigenic variation. The VSG is attached to the external face of the plasma membrane by covalent attachment of the C-terminus to a glycosylphosphatidylinositol. As the trypanosome grows, newly synthesised VSG is added to the plasma membrane by vesicle fusion to the flagellar pocket, the sole location of exo- and endocytosis. Snake venoms contain dozens of components including proteases and phospholipases. Here, we investigated the effect of Naja nigricollis on T. brucei with the aim of describing the response of the trypanosome to hydrolytic attack on the VSG. We found no evidence for VGS hydrolysis however N. nigricollis venom caused: (i) an enlargement of the flagellar pocket, (ii) the Rab11 positive endosomal compartments to adopt an abnormal dispersed localisation, and (iii) a cell cycle arrest prior to cytokinesis. A single protein family, the phospholipases A2s present in N. nigricollis venom, was necessary and sufficient for the effects. This study provides new molecular insight into T. brucei biology and possibly describes mechanisms that could be exploited for T. brucei targeting.

scholarly journals Inositol phosphate pathway controls transcription of telomeric expression sites in trypanosomes

2015 ◽  
Vol 112 (21) ◽  
pp. E2803-E2812 ◽  
Author(s):  
Igor Cestari ◽  
Ken Stuart
Keyword(s):  
Plasma Membrane ◽  
Trypanosoma Brucei ◽  
Antigenic Variation ◽  
Inositol Phosphate ◽  
Rna Polymerase I ◽  
Surface Glycoprotein ◽  
Variant Surface Glycoprotein ◽  
Activator Protein 1 ◽  
African Trypanosomes ◽  
Polymerase I

African trypanosomes evade clearance by host antibodies by periodically changing their variant surface glycoprotein (VSG) coat. They transcribe only one VSG gene at a time from 1 of about 20 telomeric expression sites (ESs). They undergo antigenic variation by switching transcription between telomeric ESs or by recombination of the VSG gene expressed. We show that the inositol phosphate (IP) pathway controls transcription of telomeric ESs and VSG antigenic switching in Trypanosoma brucei. Conditional knockdown of phosphatidylinositol 5-kinase (TbPIP5K) or phosphatidylinositol 5-phosphatase (TbPIP5Pase) or overexpression of phospholipase C (TbPLC) derepresses numerous silent ESs in T. brucei bloodstream forms. The derepression is specific to telomeric ESs, and it coincides with an increase in the number of colocalizing telomeric and RNA polymerase I foci in the nucleus. Monoallelic VSG transcription resumes after reexpression of TbPIP5K; however, most of the resultant cells switched the VSG gene expressed. TbPIP5K, TbPLC, their substrates, and products localize to the plasma membrane, whereas TbPIP5Pase localizes to the nucleus proximal to telomeres. TbPIP5Pase associates with repressor/activator protein 1 (TbRAP1), and their telomeric silencing function is altered by TbPIP5K knockdown. These results show that specific steps in the IP pathway control ES transcription and antigenic switching in T. brucei by epigenetic regulation of telomere silencing.

scholarly journals The GPI-Phospholipase C of Trypanosoma brucei Is Nonessential But Influences Parasitemia in Mice

1997 ◽  
Vol 139 (1) ◽  
pp. 103-114 ◽  
Author(s):  
Helena Webb ◽  
Nicola Carnall ◽  
Luc Vanhamme ◽  
Sylvie Rolin ◽  
Jakke Van Den Abbeele ◽  
...  
Keyword(s):  
Phospholipase C ◽  
Trypanosoma Brucei ◽  
Antigenic Variation ◽  
Surface Glycoprotein ◽  
Covalent Attachment ◽  
Mammalian Host ◽  
Surface Coat ◽  
Null Mutant

In the mammalian host, the cell surface of Trypanosoma brucei is protected by a variant surface glycoprotein that is anchored in the plasma membrane through covalent attachment of the COOH terminus to a glycosylphosphatidylinositol. The trypanosome also contains a phospholipase C (GPI-PLC) that cleaves this anchor and could thus potentially enable the trypanosome to shed the surface coat of VSG. Indeed, release of the surface VSG can be observed within a few minutes on lysis of trypanosomes in vitro. To investigate whether the ability to cleave the membrane anchor of the VSG is an essential function of the enzyme in vivo, a GPI-PLC null mutant trypanosome has been generated by targeted gene deletion. The mutant trypanosomes are fully viable; they can go through an entire life cycle and maintain a persistent infection in mice. Thus the GPI-PLC is not an essential activity and is not necessary for antigenic variation. However, mice infected with the mutant trypanosomes have a reduced parasitemia and survive longer than those infected with control trypanosomes. This phenotype is partially alleviated when the null mutant is modified to express low levels of GPI-PLC.

Bloodstream form trypanosome plasma membrane proteins: antigenic variation and invariant antigens

Parasitology ◽  
2010 ◽  
Vol 137 (14) ◽  
pp. 2029-2039 ◽  
Author(s):  
ANGELA SCHWEDE ◽  
MARK CARRINGTON
Keyword(s):  
Plasma Membrane ◽  
Trypanosoma Brucei ◽  
Antigenic Variation ◽  
Adaptive Immune System ◽  
Surface Proteins ◽  
Surface Glycoprotein ◽  
Invariant Surface ◽  
Adaptive Immune ◽  
External Face

SUMMARYTrypanosoma bruceiis exposed to the adaptive immune system and complement in the blood of its mammalian hosts. The aim of this review is to analyse the role and regulation of the proteins present on the external face of the plasma membrane in the long-term persistence of an infection and transmission. In particular, the following are addressed: (1) antigenic variation of the variant surface glycoprotein (VSG), (2) the formation of an effective VSG barrier shielding invariant surface proteins, and (3) the rapid uptake of VSG antibody complexes combined with degradation of the immunoglobulin and recycling of the VSG.

scholarly journals Developmental competence and antigen switch frequency can be uncoupled in Trypanosoma brucei

2019 ◽  
Vol 116 (45) ◽  
pp. 22774-22782 ◽  
Author(s):  
Kirsty R. McWilliam ◽  
Alasdair Ivens ◽  
Liam J. Morrison ◽  
Monica R. Mugnier ◽  
Keith R. Matthews
Keyword(s):  
Trypanosoma Brucei ◽  
Antigenic Variation ◽  
Experimental Studies ◽  
Developmental Competence ◽  
Parasite Development ◽  
Mammalian Host ◽  
Mechanical Transmission ◽  
African Trypanosomes ◽  
Infection Dynamic ◽  
Developmental Capacity

African trypanosomes use an extreme form of antigenic variation to evade host immunity, involving the switching of expressed variant surface glycoproteins by a stochastic and parasite-intrinsic process. Parasite development in the mammalian host is another feature of the infection dynamic, with trypanosomes undergoing quorum sensing (QS)-dependent differentiation between proliferative slender forms and arrested, transmissible, stumpy forms. Longstanding experimental studies have suggested that the frequency of antigenic variation and transmissibility may be linked, antigen switching being higher in developmentally competent, fly-transmissible, parasites (“pleomorphs”) than in serially passaged “monomorphic” lines that cannot transmit through flies. Here, we have directly tested this tenet of the infection dynamic by using 2 experimental systems to reduce pleomorphism. Firstly, lines were generated that inducibly lose developmental capacity through RNAi-mediated silencing of the QS signaling machinery (“inducible monomorphs”). Secondly, de novo lines were derived that have lost the capacity for stumpy formation by serial passage (“selected monomorphs”) and analyzed for their antigenic variation in comparison to isogenic preselected populations. Analysis of both inducible and selected monomorphs has established that antigen switch frequency and developmental capacity are independently selected traits. This generates the potential for diverse infection dynamics in different parasite populations where the rate of antigenic switching and transmission competence are uncoupled. Further, this may support the evolution, maintenance, and spread of important trypanosome variants such as Trypanosoma brucei evansi that exploit mechanical transmission.

scholarly journals Escaping the immune system by DNA repair and recombination in African trypanosomes

Open Biology ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 190182 ◽  
Author(s):  
Núria Sima ◽  
Emilia Jane McLaughlin ◽  
Sebastian Hutchinson ◽  
Lucy Glover
Keyword(s):  
Immune Response ◽  
Dna Repair ◽  
Trypanosoma Brucei ◽  
Antigenic Variation ◽  
Surface Glycoprotein ◽  
Variant Surface Glycoprotein ◽  
Surface Coat ◽  
African Trypanosomes ◽  
Active Expression ◽  
Expression Site

African trypanosomes escape the mammalian immune response by antigenic variation—the periodic exchange of one surface coat protein, in Trypanosoma brucei the variant surface glycoprotein (VSG), for an immunologically distinct one. VSG transcription is monoallelic, with only one VSG being expressed at a time from a specialized locus, known as an expression site. VSG switching is a predominantly recombination-driven process that allows VSG sequences to be recombined into the active expression site either replacing the currently active VSG or generating a ‘new’ VSG by segmental gene conversion. In this review, we describe what is known about the factors that influence this process, focusing specifically on DNA repair and recombination.

scholarly journals Trypanosoma brucei Interaction with Host: Mechanism of VSG Release as Target for Drug Discovery for African Trypanosomiasis

2019 ◽  
Vol 20 (6) ◽  
pp. 1484 ◽  
Author(s):  
Cláudia Moreno ◽  
Adriana Temporão ◽  
Taffarel Torres ◽  
Marcelo Sousa Silva
Keyword(s):  
Drug Discovery ◽  
Phospholipase C ◽  
Trypanosoma Brucei ◽  
Antigenic Variation ◽  
Surface Glycoprotein ◽  
Mammalian Host ◽  
African Trypanosomiasis ◽  
Variable Surface Glycoprotein ◽  
Variable Surface ◽  
Major Surface

The protozoan Trypanosoma brucei, responsible for animal and human trypanosomiasis, has a family of major surface proteases (MSPs) and phospholipase-C (PLC), both involved in some mechanisms of virulence during mammalian infections. During parasitism in the mammalian host, this protozoan is exclusively extracellular and presents a robust mechanism of antigenic variation that allows the persistence of infection. There has been incredible progress in our understanding of how variable surface glycoproteins (VSGs) are organised and expressed, and how expression is switched, particularly through recombination. The objective of this manuscript is to create a reflection about the mechanisms of antigenic variation in T. brucei, more specifically, in the process of variable surface glycoprotein (VSG) release. We firstly explore the mechanism of VSG release as a potential pathway and target for the development of anti-T. brucei drugs.

scholarly journals Expression site attenuation mechanistically links antigenic variation and development in Trypanosoma brucei

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Christopher Batram ◽  
Nicola G Jones ◽  
Christian J Janzen ◽  
Sebastian M Markert ◽  
Markus Engstler
Keyword(s):  
Trypanosoma Brucei ◽  
Histone Methylation ◽  
Antigenic Variation ◽  
Tsetse Fly ◽  
Developmental Competence ◽  
Surface Glycoprotein ◽  
G1 Phase ◽  
African Trypanosomes ◽  
Developmental Progression ◽  
Expression Site

We have discovered a new mechanism of monoallelic gene expression that links antigenic variation, cell cycle, and development in the model parasite Trypanosoma brucei. African trypanosomes possess hundreds of variant surface glycoprotein (VSG) genes, but only one is expressed from a telomeric expression site (ES) at any given time. We found that the expression of a second VSG alone is sufficient to silence the active VSG gene and directionally attenuate the ES by disruptor of telomeric silencing-1B (DOT1B)-mediated histone methylation. Three conserved expression-site-associated genes (ESAGs) appear to serve as signal for ES attenuation. Their depletion causes G1-phase dormancy and reversible initiation of the slender-to-stumpy differentiation pathway. ES-attenuated slender bloodstream trypanosomes gain full developmental competence for transformation to the tsetse fly stage. This surprising connection between antigenic variation and developmental progression provides an unexpected point of attack against the deadly sleeping sickness.

scholarly journals To the Surface and Back: Exo- and Endocytic Pathways in Trypanosoma brucei

2021 ◽  
Vol 9 ◽  
Author(s):  
Fabian Link ◽  
Alyssa R. Borges ◽  
Nicola G. Jones ◽  
Markus Engstler
Keyword(s):  
Cell Surface ◽  
Trypanosoma Brucei ◽  
Immune Evasion ◽  
Antigenic Variation ◽  
Critical Role ◽  
Surface Glycoprotein ◽  
Immune Recognition ◽  
Flagellar Pocket ◽  
Novel Technologies ◽  
Near Future

Trypanosoma brucei is one of only a few unicellular pathogens that thrives extracellularly in the vertebrate host. Consequently, the cell surface plays a critical role in both immune recognition and immune evasion. The variant surface glycoprotein (VSG) coats the entire surface of the parasite and acts as a flexible shield to protect invariant proteins against immune recognition. Antigenic variation of the VSG coat is the major virulence mechanism of trypanosomes. In addition, incessant motility of the parasite contributes to its immune evasion, as the resulting fluid flow on the cell surface drags immunocomplexes toward the flagellar pocket, where they are internalized. The flagellar pocket is the sole site of endo- and exocytosis in this organism. After internalization, VSG is rapidly recycled back to the surface, whereas host antibodies are thought to be transported to the lysosome for degradation. For this essential step to work, effective machineries for both sorting and recycling of VSGs must have evolved in trypanosomes. Our understanding of the mechanisms behind VSG recycling and VSG secretion, is by far not complete. This review provides an overview of the trypanosome secretory and endosomal pathways. Longstanding questions are pinpointed that, with the advent of novel technologies, might be answered in the near future.

scholarly journals Gene conversions mediating antigenic variation in Trypanosoma brucei can occur in variant surface glycoprotein expression sites lacking 70-base-pair repeat sequences.

1997 ◽  
Vol 17 (2) ◽  
pp. 833-843 ◽  
Author(s):  
R McCulloch ◽  
G Rudenko ◽  
P Borst
Keyword(s):  
Gene Conversion ◽  
Antigenic Variation ◽  
Surface Glycoprotein ◽  
Variant Surface Glycoprotein ◽  
Mammalian Host ◽  
Recognition Sequence ◽  
African Trypanosomes ◽  
Repeat Sequences ◽  
Active Expression ◽  
Expression Site

African trypanosomes undergo antigenic variation of their variant surface glycoprotein (VSG) coat to avoid immune system-mediated killing by their mammalian host. An important mechanism for switching the expressed VSG gene is the duplicative transposition of a silent VSG gene into one of the telomeric VSG expression sites of the trypanosome, resulting in the replacement of the previously expressed VSG gene. This process appears to be a gene conversion reaction, and it has been postulated that sequences within the expression site may act to initiate and direct the reaction. All bloodstream form expression sites contain huge arrays (many kilobase pairs) of 70-bp repeat sequences that act as the 5' boundary of gene conversion reactions involving most silent VSG genes. For this reason, the 70-bp repeats seemed a likely candidate to be involved in the initiation of switching. Here, we show that deletion of the 70-bp repeats from the active expression site does not affect duplicative transposition of VSG genes from silent expression sites. We conclude that the 70-bp repeats do not appear to function as indispensable initiation sites for duplicative transposition and are unlikely to be the recognition sequence for a sequence-specific enzyme which initiates recombination-based VSG switching.

scholarly journals Targeting the Variable Surface of African Trypanosomes with Variant Surface Glycoprotein-Specific, Serum-Stable RNA Aptamers

2003 ◽  
Vol 2 (1) ◽  
pp. 84-94 ◽  
Author(s):  
Mihaela Lorger ◽  
Markus Engstler ◽  
Matthias Homann ◽  
H. Ulrich Göringer
Keyword(s):  
Antigenic Variation ◽  
Sleeping Sickness ◽  
Rna Aptamers ◽  
Surface Glycoprotein ◽  
Variant Surface Glycoprotein ◽  
Parasite Protein ◽  
African Trypanosomes ◽  
Variable Surface ◽  
New Strategy

ABSTRACT African trypanosomes cause sleeping sickness in humans and Nagana in cattle. The parasites multiply in the blood and escape the immune response of the infected host by antigenic variation. Antigenic variation is characterized by a periodic change of the parasite protein surface, which consists of a variant glycoprotein known as variant surface glycoprotein (VSG). Using a SELEX (systematic evolution of ligands by exponential enrichment) approach, we report the selection of small, serum-stable RNAs, so-called aptamers, that bind to VSGs with subnanomolar affinity. The RNAs are able to recognize different VSG variants and bind to the surface of live trypanosomes. Aptamers tethered to an antigenic side group are capable of directing antibodies to the surface of the parasite in vitro. In this manner, the RNAs might provide a new strategy for a therapeutic intervention to fight sleeping sickness.

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