The online version of this article (https://doi.org/10.1186/s12936-018-2176-x) contains supplementary material, which is available to authorized users.
Genetic diversity of the three important antigenic proteins, namely thrombospondin-related anonymous protein (TRAP), apical membrane antigen 1 (AMA1), and 6-cysteine protein (P48/45), all of which are found in various developmental stages of Plasmodium parasites is crucial for targeted vaccine development. While studies related to the genetic diversity of these proteins are available for Plasmodium falciparum and Plasmodium vivax, barely enough information exists regarding Plasmodium malariae. The present study aims to demonstrate the genetic variations existing among these three genes in P. malariae by analysing their diversity at nucleotide and protein levels.
Three surface protein genes were isolated from 45 samples collected in Thailand (N = 33), Myanmar (N = 8), and Lao PDR (N = 4), using conventional polymerase chain reaction (PCR) assay. Then, the PCR products were sequenced and analysed using BioEdit, MEGA6, and DnaSP programs.
The average pairwise nucleotide diversities (π) of P. malariae trap, ama1, and p48/45 were 0.00169, 0.00413, and 0.00029, respectively. The haplotype diversities (Hd) of P. malariae trap, ama1, and p48/45 were 0.919, 0.946, and 0.130, respectively. Most of the nucleotide substitutions were non-synonymous, which indicated that the genetic variations of these genes were maintained by positive diversifying selection, thus, suggesting their role as a potential target of protective immune response. Amino acid substitutions of P. malariae TRAP, AMA1, and P48/45 could be categorized to 17, 20, and 2 unique amino-acid variants, respectively. For further vaccine development, carboxyl terminal of P48/45 would be a good candidate according to conserved amino acid at low genetic diversity (π = 0.2–0.3).
High mutational diversity was observed in P. malariae trap and ama1 as compared to p48/45 in P. malariae samples isolated from Thailand, Myanmar, and Lao PDR. Taken together, these results suggest that P48/45 might be a good vaccine candidate against P. malariae infection because of its sufficiently low genetic diversity and highly conserved amino acids especially on the carboxyl end.
Additional file 1. Specific primers and PCR conditions for isolation of 3 surface protein genes.
Additional file 2. Domain prediction of P. malariae TRAP, AMA1, and P48/45 using InterPro.
Additional file 3. Accession numbers of amino acid sequences and gene IDs of six Plasmodium TRAP, AMA1, and P48/45 obtained from database.
Additional file 4. Amino acid identity of non-cytoplasmic region TRAP, AMA1, and P48/45 within six Plasmodium species.
Additional file 5. Maximum likelihood trees of six human malaria parasites based on amino acid sequences of TRAP, AMA1, and P48/45.
Additional file 6. PmTRAP1, PmAMA1, and PmP48/45 variant frequencies in Thailand, Myanmar, and Lao PDR.
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- Genetic diversity of three surface protein genes in Plasmodium malariae from three Asian countries
Nicholas P. J. Day
Arjen M. Dondorp
- BioMed Central
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