Analysis of Single Nucleotide polymorphisms at the Plasmodium vivax Apical Membrane Antigen 1 (PvAMA1) locus among Sri Lankan isolates.

Abstract

The assessment of genetic structure among parasite populations has significant relevance for both the control and epidemiology of malaria; in particular, examining diversity among antigenic loci rs crucial for effective local vaccine development. Here, we characterized the distribution of SNPs in both the coding and non-coding regions of the eminent vaccine candidate, Plasmodium vivax AMA-'I, in Sri Lanka. An extensive analysis of this type has yet to be conducted from field isolates in this region. Furthermore, this is the first time polymorphisms across the entire coding sequence of PvAMA-1' as well as its upstream region, have been investigated. Blood samples were collected from patients presenting at clinics in both non-endemic (Colombo) and endemic settings in Sri Lanka(Kataragama and ,Anuradhapura). 30 single clone infections were selected following RFLP analysis at the MSP-54 locus. SNPs, the majority of which were non-synonymous, were found amongst all three ectodomains of PvAMAl, but were notably absent in the pro-domain and transmembrane/carboxy-terminal tail regions of the gene. Polymorphisms across ectodomains I and ll specifically, show significant deviance from neutrality (McDonald-Kreitman test p<O.o5), consistent with previous findings that this antigen is likely under host immune selection. Each polymorphic site uncovered here was also conserved among vivax isolates from various localities in Africa and Asia. When these residues were mapped onto the recently published PvAM.Al crystal structure (Pizarro, 2OO5), the maiority clustered on the outer surface of the protein; two electrostatically interesting polymorphisms were also localized to a putative receptor-binding site of the protein. Finally, the SNP profile of the 5' upstream region of PvAMAI was characterized following sequence analysis of a -7OObp segment upstream of its start codon in five isolates. Only two SNPs, one single-site deletion, and two insertion-deletion repeats were evident, representing a polymorphism frequency that is significantly lower than that found in the coding region of PvAM,A-!