RESUMEN
Worldwide malaria risk due to Plasmodium vivax makes development of vaccine against P. vivax, a high priority. Serine Repeat Antigen of P. vivax (PvSERA) is a multigene family of blood stage proteins with 12 homologues. Sequence diversity studies are important for understanding them as potential vaccine candidates. No information on N-terminal diversity of these genes is available in literature. In this paper, we evaluate the genetic polymorphism of N-terminal regions of the highly expressed member PvSERA4 and PvSERA5 genes from Indian field isolates. Our results show that PvSERA4 has deletions and insertions in Glutamine rich tetrameric repeat units contributing to its diversity. PvSERA5 also exhibits high genetic diversity with non-synonymous substitutions leading to identification of novel haplotypes from India. Our first report helps in elucidating the allelic variants of PvSERA genes in this region and contributes to evaluating their efficacy as vaccine candidates.
Asunto(s)
Antígenos de Protozoos/genética , Haplotipos , Plasmodium vivax/genética , Polimorfismo Genético , Secuencias Repetitivas de Aminoácido , Alelos , Secuencia de Aminoácidos , Eritrocitos/parasitología , Exones , Humanos , India/epidemiología , Intrones , Malaria Vivax/epidemiología , Malaria Vivax/parasitología , Datos de Secuencia Molecular , Filogenia , Plasmodium vivax/clasificación , Alineación de Secuencia , Análisis de Secuencia de ADNRESUMEN
The burden of Plasmodium vivax malaria is huge in India, affecting a large population annually. Recent reports of P. vivax contributing to severe illness and death, makes vaccine research on P. vivax malaria, a high priority. Extent of sequence variation in antigen coding genes is known to be a major hurdle in vaccine initiatives against malaria. Serine repeat antigens of Plasmodium are promising asexual blood stage vaccine candidates against malaria and have been implicated to have a key role in merozoite invasion and egress. Among the P. vivax SERA proteins, SERA4 and SERA5 are the major transcribed members in erythrocytic stages, making them encouraging candidates to be explored for their polymorphism and vaccine potential. Earlier reports suggest that diversity in these PvSERA antigens is localized to the C-terminal region of the proteins. Hence, genetic diversity study of this region seems prudent. Moreover, as there are no reports available from India, the present study aims to investigate the polymorphism in the C-terminal region of two highly transcribed members PvSERA4 and PvSERA5 in Indian field isolates. Our result of PvSERA5 demonstrates extensive genetic diversity, with major deletions, insertions and SNPs and signifies the gene to be under positive selection. On the other hand, high sequence conservation was seen in the PvSERA4 C-terminal region in Indian field isolates which was contrasting to earlier report from Thailand where they have shown diversity. Research data showcased in this study will greatly aid in gaining better understanding of antigenic variations, immune mediated selection mechanisms and the functional significance of these two vivax proteins. This study also makes a striking contribution towards understanding the antigenic repertoire of PvSERA genes in Indian isolates.
Asunto(s)
Antígenos de Protozoos/genética , Variación Genética/genética , Malaria Vivax/parasitología , Plasmodium vivax/genética , Adulto , Secuencia de Aminoácidos , Antígenos de Protozoos/inmunología , Secuencia de Bases , ADN Protozoario/sangre , ADN Protozoario/química , ADN Protozoario/aislamiento & purificación , Humanos , India , Desequilibrio de Ligamiento , Malaria Vivax/sangre , Malaria Vivax/prevención & control , Datos de Secuencia Molecular , Mutación , Plasmodium vivax/inmunología , Reacción en Cadena de la Polimerasa , Polimorfismo Genético/genética , ARN Ribosómico 18S/genética , Alineación de SecuenciaRESUMEN
Plasmodium vivax malaria is geographically the most widely distributed and prevalent form of human malaria. The development of drug resistance by the parasite to existing drugs necessitates higher focus to explore and identify new drug targets. Plasmodial proteases have key roles in parasite biology and are involved in nutritional uptake, egress from infected reticulocytes, and invasion of the new target erythrocytes. Serine repeat antigens (SERA) of Plasmodium are parasite proteases that remain attractive drug targets and are important vaccine candidates due to their high expression profiles in the blood stages. SERA proteins have a unique putative papain-like cysteine protease motif that has either serine or cysteine in its active site. In P. vivax, PvSERA4 is the highest transcribed member of this multigene family. In this study, we have investigated the genetic polymorphism of PvSERA4 central protease domain and deduced its 3D model by homology modeling and also performed MD simulations to acquire refined protein structure. Sequence analysis of protease domain of PvSERA4 from Indian field isolates reveals that the central domain is highly conserved. The high sequence conservation of the PvSERA4 enzyme domain coupled with its high expression raises the possibility of it having a critical role in parasite biology and hence, being a reliable target for new selective inhibitor-based antimalarial chemotherapeutics. The 3D model showed the presence of an unusual antiparallel Beta hairpin motif between catalytic residues similar to hemoglobin binding motif of Plasmodial hemoglobinases. Our PvSERA4 model will aid in designing structure-based inhibitors against this enzyme.