Genetic Diversity in New Members of the Reticulocyte Binding Protein Family in Thai Plasmodium vivax Isolates

Abstract

Background Plasmodium vivax merozoites specifically invade reticulocytes. Until recently, two reticulocyte-binding proteins (Pvrbp1 and Pvrbp2) expressed at the apical pole of the P. vivax merozoite were considered to be involved in reticulocyte recognition. The genome sequence recently obtained for the Salvador I (Sal-I) strain of P. vivax revealed additional genes in this family, and in particular Pvrbp2a, Pvrbp2b (Pvrbp2 has been renamed as Pvrbp2c) and two pseudogenes Pvrbp2d and Pvrbp3. It had been previously found that Pvrbp2c is substantially more polymorphic than Pvrbp1. The primary goal of this study was to ascertain the level of polymorphism of these new genes.Methodology/Principal FindingsThe sequence of the Pvrbp2a, Pvrbp2b, Pvrbp2d and Pvrbp3 genes were obtained by amplification/cloning using DNA purified from four isolates collected from patients that acquired the infection in the four cardinal regions of Thailand (west, north, south and east). An additional seven isolates from western Thailand were analyzed for gene copy number variation. There were significant polymorphisms exhibited by these genes (compared to the reference Sal-I strain) with the ratio of mutations leading to a non-synonymous or synonymous amino acid change close to 3∶1 for Pvrbp2a and Pvrbp2b. Although the degree of polymorphism exhibited by these two genes was higher than that of Pvrbp1, it did not reach the exceptional diversity noted for Pvrbp2c. It was interesting to note that variations in the copy number of Pvrbp2a and Pvrbp2b occurred in some isolates.Conclusions/SignificanceThe evolution of different members of the Pvrbp2 family and their relatively high degree of polymorphism suggests that the proteins encoded by these genes are important for parasite survival and are under immune selection. Our data also shows that there are highly conserved regions in rbp2a and rbp2b, which might provide suitable targets for future vaccine development against the blood stage of P. vivax.

Gene Models, Expression Repertoire, and Immune Response of Plasmodium vivax Reticulocyte Binding Proteins

“…Previous analyses of several Pvrbp sequences have revealed evidence of positive diversifying selection ( 14 , 29 ). These studies found a strikingly high degree of polymorphism in Pvrbp2c relative to other Pvrbp genes.…”

The association of Duffy binding protein region II polymorphisms and its antigenicity in Plasmodium vivax isolates from Thailand

“…A significant portion of malaria cases in Thailand occur among temporary migrant workers from bordering countries presenting a major challenge to prevention and control of malaria in Thailand. The genetic polymorphism in the Reticulocyte Binding Protein (RBP), Merozoite Surface Protein 5 (MSP-5) and Merozoite Surface Protein 3 α/β of P. vivax Thai isolates were analyzed in previous studies and showed high levels of genetic polymorphism (23–26). However, the information on the nature and extent of population diversity as well as the antigenic character of malaria parasites in Thailand is still limited.…”

Identification of Immunodominant B-cell Epitope Regions of Reticulocyte Binding Proteins in <i>Plasmodium vivax</i> by Protein Microarray Based Immunoscreening

“…RBL proteins feature a small and large exon separated by a small intron, and the small exon encodes the signal peptide [ 19 , 20 ]. The complete gene sequence of P. vivax Salvador I (Sal-1) strain comprises genes for 11 P. vivax reticulocyte binding proteins (PvRBP) as well as 2 pseudogenes [ 14 , 21 ]. Five of these genes are highly expressed in schizont stage during the erythrocytic stage of P. vivax parasites [ 22 , 23 ].…”