Biology subjects

Aresta-Branco, F.

Publications and source records attributed to Aresta-Branco, F..

5 recordsLinked to original sources

bioRxiv2023

A Structural Classification of the Variant Surface Glycoproteins of the African Trypanosome

Long-term immune evasion by the African trypanosome is achieved through repetitive cycles of surface protein replacement with antigenically distinct versions of the dense Variant Surface Glycoprotein (VSG) coat. Thousands of VSG genes and pseudo-genes exist in the parasite genome that, together with genetic recombination mechanisms, allow for essentially unlimited immune escape from the hosts adaptive immune system. The diversity space of the "VSGnome" at the protein level was thought to be limited to a few related folds whose structures were determined more than 30 years ago. However, recent progress has shown that the VSGs possess significantly more architectural variation than had been appreciated. Here we combine experimental X-ray crystallography with deep-learning structural prediction using Alphafold to produce models of hundreds of VSG proteins. We classify the VSGnome into groups based on protein architecture and oligomerization state, contextualize recent bioinformatics clustering schemes, and extensively map VSG-diversity space. We demonstrate that in addition to the structural variability and post-translational modifications observed thus far, VSGs are also characterized by variations in oligomerization state and possess inherent flexibility and alternative conformations, lending additional variability to what is exposed to the immune system. Finally, these additional experimental structures and the hundreds of Alphafold predictions confirm that the molecular surfaces of the VSGs remain distinct from variant to variant, supporting the hypothesis that protein surface diversity is central to the process of antigenic variation used by this organism during infection.

microbiology↗

bioRxiv2022

Structural and Immunological Similarities Between the Metacyclic and Bloodstream Form Variant Surface Glycoproteins of the African Trypanosome

During infection of mammalian hosts, African trypanosomes thwart immunity using antigenic variation of the dense Variant Surface Glycoprotein (VSG) coat, accessing a large repertoire of thousands of genes and pseudogenes and switching to antigenically distinct copies. The parasite is transferred to mammalian hosts through the bite of the tsetse fly. In the salivary glands of the fly, the pathogen adopts the metacyclic form and expresses a limited repertoire of VSG genes specific to that developmental stage. It has remained unknown whether the metacyclic VSGs possess distinct properties associated with this particular and discrete phase of the parasite life cycle. We show here using bioinformatic, crystallographic, and immunological analyses of three metacyclic VSGs that they closely mirror the known classes of bloodstream form VSGs both in structure and in the immunological responses they elicit.

microbiology↗

bioRxiv2021

Immunodominant surface epitopes power immune evasion in the African trypanosome

The African trypanosome survives the immune response of its mammalian host by antigenic variation of its major surface antigen (the Variable Surface Glycoprotein, or VSG). Here we describe the antibody repertoires elicited by different VSGs. We show that the repertoires are highly restricted, and are directed predominantly to distinct epitopes on the surface of the VSGs. They are also highly discriminatory: minor alterations within these exposed epitopes confer antigenically-distinct properties to these VSGs and elicit different repertoires. We propose that the patterned and repetitive nature of the VSG coat focuses host immunity to a restricted set of immunodominant epitopes per VSG, eliciting a highly stereotyped response, minimizing cross reactivity between different VSGs and facilitating prolonged immune evasion through epitope variation.

immunology↗

bioRxiv2021

The effect of in vitro culture on unicellular eukaryotes: adaptation of Trypanosoma brucei brucei bloodstream forms results in gene copy-number changes.

Most researchers who study unicellular eukaryotes work with an extremely limited number of laboratory-adapted isolates that were obtained from the field decades ago, but the effects of passage in laboratory rodents, and adaptation to in vitro culture, have been little studied. For example, the vast majority of studies of Trypanosoma brucei biology have concentrated on just two strains, Lister 427 and EATRO1125, which were taken from the field over half a century ago and have since have undergone innumerable passages in rodents and culture. We here describe two new Trypanosoma brucei brucei strains. MAK65 and MAK98, which have undergone only 3 rodent passages since isolation from Ugandan cattle. High-coverage sequencing revealed that adaptation of the parasites to culture was accompanied by changes in gene copy numbers. T. brucei has so far been considered to be uniformly diploid, but we also found trisomy of chromosome 5 not only in one Lister 427 culture, but also in the MAK98 field isolate. Trisomy of chromosome 6, and increased copies of other chromosome segments, were also seen in established cultured lines. The two new T. brucei strains should be useful to researchers interested in trypanosome differentiation and pathogenicity. Initial results suggested that the two strains have differing infection patterns in rodents. MAK65 is uniformly diploid and grew more reproducibly in bloodstream-form culture than MAK98.

genomics↗

bioRxiv2020

N6-methyladenosine in poly(A) tails stabilize VSG transcripts

RNA modifications are important regulators of gene expression. In Trypanosoma brucei, transcription is polycistronic and thus most regulation happens post-transcriptionally. N6-methyladenosine (m6A) has been detected in this parasite, but its function remains unknown. Here we show that [~]50% of the m6A is located in the poly(A) tail of the monoallelically expressed Variant Surface Glycoprotein (VSG) transcript. m6A residues are removed from the VSG poly(A) tail prior to deadenylation and mRNA degradation. Using genetic tools, we identified a 16-mer motif in the 3UTR of VSG that acts as a cis-acting motif required for inclusion of m6A in the poly(A) tail. Removal of this motif from the VSG 3 UTR results in poly(A) tails lacking m6A, rapid deadenylation and mRNA degradation. To our knowledge this is the first identification of an RNA modification in the poly(A) tail of any eukaryote, uncovering a novel post-transcriptional mechanism of gene regulation.

molecular biology↗