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-!
