Plasmodium falciparum: worldwide sequence diversity and evolution of the malaria vaccine candidate merozoite surface protein-2 (MSP-2) |
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Authors: | Ferreira Marcelo U Hartl Daniel L |
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Institution: | Department of Parasitology, Institute of Biomedical Sciences, University of S?o Paulo, Av. Prof. Lineu Prestes 1374, 05508-900 S?o Paulo (SP), Brazil. muferrei@usp.br |
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Abstract: | We examined patterns and putative mechanisms of sequence diversification in the merozoite surface protein-2 (MSP-2) of Plasmodium falciparum, a major dimorphic malaria vaccine candidate antigen, by analyzing 448 msp-2 alleles from all continents. We describe several nucleotide replacements, insertion and deletion events, frameshift mutations, and proliferations of repeat units that generate the extraordinary diversity found in msp-2 alleles. We discuss the role of positive selection exerted by naturally acquired type- and variant-specific immunity in maintaining the observed levels of polymorphism and suggest that this is the most likely explanation for the significant excess of nonsynonymous nucleotide replacements found in dimorphic msp-2 domains. Hybrid sequences created by meiotic recombination between alleles of different dimorphic types were observed in few (3.1%) isolates, mostly from Africa. We found no evidence for an extremely ancient origin of allelic dimorphism at the msp-2 locus, predating P. falciparum speciation, in contrast with recent findings for other surface malarial antigens. |
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Keywords: | Malaria MSP-2 Evolution Recombination Allelic dimorphism Antigenic diversity Vaccine development bp base pairs MSP-1 merozoite surface protein-1 MSP-2 merozoite surface protein-2 Myr million years RHR repeat homology region SD standard deviation SE standard error of the mean TMRCA time to the most recent common ancestor |
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