Estudio del polimorfismo de los genes que codifican para las proteínas de superficie del merozoito (msp)-7c, -7h y -7i de plasmodium vivax a partir de aislados colombianos

Se evaluó el nivel y la distribución del polimorfismo de los genes msp-7C, msp- 7H y msp-7I en aislados naturales de Plasmodium vivax y se detectó las fuerzas evolutivas que determinaban este patrón de variación genética en la población parasitaria de individuos infectados en varias regiones de Colombia. / Abstract: The level and distribution of genetic polymorphism in msp-7C, msp-7H and msp-7I genes from a natural population of Plasmodium vivax was assessed. The evolutionary forces that determined this pattern of genetic variation in parasite samples from Colombian P. vivax-infected individuals were also detected.Maestrí

Selección natural en genes de Plasmodium vivax y su potencial uso en una vacuna antimalárica

Plasmodium vivax, es un endoparásito de origen Asiático que se dispersó alrededor del mundo y, actualmente, es predominante en las regiones tropicales y subtropicales del planeta que se encuentran entre los 15 y 16 °C. P. vivax, presenta una importancia biomédica dado que es el segundo agente responsable de malaria en humanos. Aunque numerosos esfuerzos se han realizado para disminuir el impacto de esta enfermedad, las condiciones sociales y económicas de los lugares más afectados, sumado a los conflictos sociales y políticos en varias áreas endémicas, hacen del control y eliminación de este parásito una tarea nada fácil. Como si esto no fuera suficiente, la aparición de resistencia a los insecticidas por parte del vector trasmisor, así como de parásitos resistentes a los antimaláricos, podría provocar una recurrencia de esta enfermedad. Teniendo en cuenta lo anterior, nuevas estrategias que permitan disminuir la incidencia de malaria por P. vivax se hacen prioritarias. Una de las alternativas que podría ayudar al control de la malaria es el desarrollo de una vacuna contra los patógenos que la causan. Sin embargo, la elevada diversidad genética que P. vivax presenta, ha generado uno de los retos a afrontar para el diseño de una vacuna completamente efectiva. Actualmente, se han descrito varios antígenos potenciales candidatos a vacuna contra P. vivax. No obstante, la diversidad genética de un reducido número de estos antígenos ha sido evaluada, debido a los requerimientos de tiempo y recursos económicos. Adicionalmente, poco se sabe acerca del rol real de estos antígenos durante el proceso de invasión de este parasito a las células hospederas. Es por esto, que nuevos enfoques, que permitan en un menor tiempo y a bajo costo identificar las regiones de estos antígenos conservadas por selección natural (usualmente asociadas con regiones funcionales) se hacen necesarios. Estos nuevos enfoques podrían entonces servir como punto de partida para la identificación o priorización de nuevos y promisorios candidatos vacunales. Este trabajo presenta los resultados un enfoque alternativo que permite hacer un acercamiento a la diversidad genética de antígenos de P. vivax, determinando regiones bajo selección negativa, para ser consideradas durante el diseño de una vacuna completamente efectiva. Aunque este enfoque se utilizó para P. vivax, este podría también ser aplicado en otros organismos.Plasmodium vivax, an endoparasite that arose in Asia and spread around the world, has biomedical importance given that it is the second most important human-malaria parasite. Although efforts have been made to reduce the impact of this disease, the social and economic conditions of the most affected places, together with social and political conflicts in several endemic areas, make the parasite control and elimination a laborious task. The emergence of insecticide resistance by the transmitting vector as well as antimalarialresistant parasites worsen the problem. Therefore, new alternatives to allow reducing the incidence of the disease have become a priority. An antimalarial vaccine development against the causal pathogens has been proposed as a cost-effective intervention which would help in controlling malaria. However, the high P. vivax genetic diversity remains as one of the challenges to overcome for the design of afully effective vaccine. Currently, several potential P. vivax vaccine candidates have been described. Nevertheless, the genetic diversity of a small number of them has been assessed, due to the high amount of time and economic resources required. Additionally, there is a modest knowledge about the real role of these antigens during the invasion process of target cells since maintaining an in vitro culture of this parasite species is particularly difficult. Therefore, new approaches that allow identifying conserved regions by natural selection which are frequently associated with functional importance, might be used as a starting point for the identification or prioritization of new potential vaccine candidates. This work presents a new approach to assess the genetic diversity of potential candidate antigens, determining negatively selected regions that can then be considered for designing a fully effective vaccine. This approach is not limited to P. vivax and could be useful in other microorganisms

Low genetic diversity in the locus encoding the Plasmodium vivax P41 protein in Colombia's parasite population

Background: The development of malaria vaccine has been hindered by the allele-specific responses produced by some parasite antigens' high genetic diversity. Such antigen genetic diversity must thus be evaluated when designing a completely effective vaccine. Plasmodium falciparum P12, P38 and P41 proteins have red blood cell binding regions in the s48/45 domains and are located on merozoite surface, P41 forming a heteroduplex with P12. These three genes have been identified in Plasmodium vivax and share similar characteristics with their orthologues in Plasmodium falciparum. Plasmodium vivax pv12 and pv38 have low genetic diversity but pv41 polymorphism has not been described.Results: Similarly to other members of the 6-Cys family, pv41 had low genetic polymorphism. pv41 3′-end displayed the highest nucleotide diversity value; several substitutions found there were under positive selection. Negatively selected codons at inter-species level were identified in the s48/45 domains; p41 would thus seem to have functional/structural constraints due to the presence of these domains.Methods. The present study was aimed at evaluating the P. vivax p41 (pv41) gene's polymorphism. DNA sequences from Colombian clinical isolates from pv41 gene were analysed for characterising and studying the genetic diversity and the evolutionary forces that produced the variation pattern so observed.Conclusions: In spite of the functional constraints of Pv41 s48/45 domains, immune system pressure seems to have allowed non-synonymous substitutions to become fixed within them as an adaptation mechanism; including Pv41 s48/45 domains in a vaccine should thus be carefully evaluated due to these domains containing some allele variants. © 2014Forero-Rodríguez et al.; licensee BioMed Central Ltd

Size polymorphism and low sequence diversity in the locus encoding the Plasmodium vivax rhoptry neck protein 4 (PvRON4) in Colombian isolates

Background: Designing a vaccine against Plasmodium vivax has focused on selecting antigens involved in invasion mechanisms that must have domains with low polymorphism for avoiding allele-specific immune responses. The rhoptry neck protein 4 (RON4) forms part of the tight junction, which is essential in the invasion of hepatocytes and/or erythrocytes; however, little is known about this locus’ genetic diversity. Methods: DNA sequences from 73 Colombian clinical isolates from pvron4 gene were analysed for characterizing their genetic diversity; pvron4 haplotype number and distribution, as well as the evolutionary forces determining diversity pattern, were assessed by population genetics and molecular evolutionary approaches. Results: ron4 has low genetic diversity in P. vivax at sequence level; however, a variable amount of tandem repeats at the N-terminal region leads to extensive size polymorphism. This region seems to be exposed to the immune system. The central region has a putative esterase/lipase domain which, like the protein’s C-terminal fragment, is highly conserved at intra- and inter-species level. Both regions are under purifying selection. Conclusions: pvron4 is the locus having the lowest genetic diversity described to date for P. vivax. The repeat regions in the N-terminal region could be associated with immune evasion mechanisms while the central region and the C-terminal region seem to be under functional or structural constraint. Bearing such results in mind, the PvRON4 central and/or C-terminal portions represent promising candidates when designing a subunit-based vaccine as they are aimed at avoiding an allele-specific immune response, which might limit vaccine efficacy. © 2016 The Author(s)

Evidence of functional divergence in MSP7 paralogous proteins : a molecular-evolutionary and phylogenetic analysis

Background: The merozoite surface protein 7 (MSP7) is a Plasmodium protein which is involved in parasite invasion; the gene encoding it belongs to a multigene family. It has been proposed that MSP7 paralogues seem to be functionally redundant; however, recent experiments have suggested that they could have different roles. Results: The msp7 multigene family has been described in newly available Plasmodium genomes; phylogenetic relationships were established in 12 species by using different molecular evolutionary approaches for assessing functional divergence amongst MSP7 members. Gene expansion and contraction rule msp7 family evolution; however, some members could have had concerted evolution. Molecular evolutionary analysis showed that relaxed and/or intensified selection modulated Plasmodium msp7 paralogous evolution. Furthermore, episodic diversifying selection and changes in evolutionary rates suggested that some paralogous proteins have diverged functionally. Conclusions: Even though msp7 has mainly evolved in line with a birth-and-death evolutionary model, gene conversion has taken place between some paralogous genes allowing them to maintain their functional redundancy. On the other hand, the evolutionary rate of some MSP7 paralogs has become altered, as well as undergoing relaxed or intensified (positive) selection, suggesting functional divergence. This could mean that some MSP7s can form different parasite protein complexes and/or recognise different host receptors during parasite invasion. These results highlight the importance of this gene family in the Plasmodium genus. © 2016 The Author(s)

Heterogeneous genetic diversity pattern in Plasmodium vivax genes encoding merozoite surface proteins (MSP) -7E, -7F and -7L

Background: The msp-7 gene has become differentially expanded in the Plasmodium genus; Plasmodium vivax has the highest copy number of this gene, several of which encode antigenic proteins in merozoites. Methods: DNA sequences from thirty-six Colombian clinical isolates from P. vivax (pv) msp-7E, -7F and -7L genes were analysed for characterizing and studying the genetic diversity of these pvmsp-7 members which are expressed during the intra-erythrocyte stage; natural selection signals producing the variation pattern so observed were evaluated. Results: The pvmsp-7E gene was highly polymorphic compared to pvmsp-7F and pvmsp-7L which were seen to have limited genetic diversity; pvmsp-7E polymorphism was seen to have been maintained by different types of positive selection. Even though these copies seemed to be species-specific duplications, a search in the Plasmodium cynomolgi genome (P. vivax sister taxon) showed that both species shared the whole msp-7 repertoire. This led to exploring the long-term effect of natural selection by comparing the orthologous sequences which led to finding signatures for lineage-specific positive selection. Conclusions: The results confirmed that the P. vivax msp-7 family has a heterogeneous genetic diversity pattern; some members are highly conserved whilst others are highly diverse. The results suggested that the 3′-end of these genes encode MSP-7 proteins' functional region whilst the central region of pvmsp-7E has evolved rapidly. The lineage-specific positive selection signals found suggested that mutations occurring in msp-7s genes during host switch may have succeeded in adapting the ancestral P. vivax parasite population to humans. © 2014 Garzón-Ospina et al

Genetic diversity and selection in three plasmodium vivax merozoite surface protein 7 (pvmsp-7) genes in a colombian population

A completely effective vaccine for malaria (one of the major infectious diseases worldwide) is not yet available; different membrane proteins involved in parasite-host interactions have been proposed as candidates for designing it. It has been found that proteins encoded by the merozoite surface protein (msp)-7 multigene family are antibody targets in natural infection; the nucleotide diversity of three Pvmsp-7 genes was thus analyzed in a Colombian parasite population. By contrast with P. falciparum msp-7 loci and ancestral P. vivax msp-7 genes, specie-specific duplicates of the latter specie display high genetic variability, generated by single nucleotide polymorphisms, repeat regions, and recombination. At least three major allele types are present in Pvmsp-7C, Pvmsp-7H and Pvmsp-7I and positive selection seems to be operating on the central region of these msp-7 genes. Although this region has high genetic polymorphism, the C-terminus (Pfam domain ID: PF12948) is conserved and could be an important candidate when designing a subunit-based antimalarial vaccine

Identifying potential Plasmodium vivax sporozoite stage vaccine candidates : An analysis of genetic diversity and natural selection

Parasite antigen genetic diversity represents a great obstacle when designing a vaccine against malaria caused by Plasmodium vivax. Selecting vaccine candidate antigens has been focused on those fulfilling a role in invasion and which are conserved, thus avoiding specific-allele immune responses. Most antigens described to date belong to the blood stage, thereby blocking parasite development within red blood cells, whilst studying antigens from other stages has been quite restricted. Antigens from different parasite stages are required for developing a completely effective vaccine; thus, pre-erythrocyte stage antigens able to block the first line of infection becoming established should also be taken into account. However, few antigens from this stage have been studied to date. Several P. falciparum sporozoite antigens are involved in invasion. Since 77% of genes are orthologous amongst Plasmodium parasites, P. vivax sporozoite antigen orthologs to those of P. falciparum might be present in its genome. Although these genes might have high genetic diversity, conserved functionally-relevant regions (ideal for vaccine development) could be predicted by comparing genetic diversity patterns and evolutionary rates. This study was thus aimed at searching for putative P. vivax sporozoite genes so as to analyse their genetic diversity for determining their potential as vaccine candidates. Several DNA sequence polymorphism estimators were computed at each locus. The evolutionary force (drift, selection and recombination) drawing the genetic diversity pattern observed was also determined by using tests based on polymorphism frequency spectrum as well as the type of intra- and inter-species substitutions. Likewise, recombination was assessed both indirectly and directly. The results showed that sporozoite genes were more conserved than merozoite genes evaluated to date. Putative domains implied in cell traversal, gliding motility and hepatocyte interaction had a negative selection signal, being conserved amongst different species in the genus. PvP52, PvP36, PvSPATR, PvPLP1, PvMCP1, PvTLP, PvCelTOS, and PvMB2 antigens or functionally restricted regions within them would thus seem promising vaccine candidates and could be used when designing a pre-erythrocyte and/or multi-stage vaccine against P. vivax to avoid allele-specific immune responses that could reduce vaccine efficacy. © 2018 Garzón-Ospina, Buitrago, Ramos and Patarroyo

PvGAMA reticulocyte binding activity: predicting conserved functional regions by natural selection analysis

Background: Adhesin proteins are used by Plasmodium parasites to bind and invade target cells. Hence, characterising molecules that participate in reticulocyte interaction is key to understanding the molecular basis of Plasmodium vivax invasion. This study focused on predicting functionally restricted regions of the P. vivax GPI-anchored micronemal antigen (PvGAMA) and characterising their reticulocyte binding activity. Results: The pvgama gene was initially found in P. vivax VCG-I strain schizonts. According to the genetic diversity analysis, PvGAMA displayed a size polymorphism very common for antigenic P. vivax proteins. Two regions along the antigen sequence were highly conserved among species, having a negative natural selection signal. Interestingly, these regions revealed a functional role regarding preferential target cell adhesion. Conclusions: To our knowledge, this study describes PvGAMA reticulocyte binding properties for the first time. Conserved functional regions were predicted according to natural selection analysis and their binding ability was confirmed. These findings support the notion that PvGAMA may have an important role in P. vivax merozoite adhesion to its target cells. © 2017 The Author(s)

On the Evolution and Function of Plasmodium vivax Reticulocyte Binding Surface Antigen (pvrbsa)

The RBSA protein is encoded by a gene described in Plasmodium species having tropism for reticulocytes. Since this protein is antigenic in natural infections and can bind to target cells, it has been proposed as a potential candidate for an anti-Plasmodium vivax vaccine. However, genetic diversity (a challenge which must be overcome for ensuring fully effective vaccine design) has not been described at this locus. Likewise, the minimum regions mediating specific parasite-host interaction have not been determined. This is why the rbsa gene’s evolutionary history is being here described, as well as the P. vivax rbsa (pvrbsa) genetic diversity and the specific regions mediating parasite adhesion to reticulocytes. Unlike what has previously been reported, rbsa was also present in several parasite species belonging to the monkey-malaria clade; paralogs were also found in Plasmodium parasites invading reticulocytes. The pvrbsa locus had less diversity than other merozoite surface proteins where natural selection and recombination were the main evolutionary forces involved in causing the observed polymorphism. The N-terminal end (PvRBSA-A) was conserved and under functional constraint; consequently, it was expressed as recombinant protein for binding assays. This protein fragment bound to reticulocytes whilst the C-terminus, included in recombinant PvRBSA-B (which was not under functional constraint), did not. Interestingly, two PvRBSA-A-derived peptides were able to inhibit protein binding to reticulocytes. Specific conserved and functionally important peptides within PvRBSA-A could thus be considered when designing a fully-effective vaccine against P. vivax