Diversity in the thrombospondin-related adhesive protein gene (TRAP) of Plasmodium vivax

We analyzed 22 clinical isolates of Plasmodium vivax from Thailand and 17 f rom Brazil to investigate the extent of sequence variation in the thrombosp ondin-related adhesive protein of Plasmodium vivax (PvTRAP), a homologue of P. falciparum TRAP (PfTRAP) which has been considered to be a promising va ccine candidate. In total 54 haplotypes were identified from 73 distinct ge ne clones. Coexistence of different PvTRAP in circulation occurred in 10 an d 13 isolates from Thailand and Brazil, respectively. Forty out of 48 subst ituted nucleotides are non-synonymous changes. Most of the substituted resi dues reside in the von Willebrand factor type A-domain (region II), a sulfa ted glycosaminoglycan-binding domain (region III) and a proline-rich region (region IV). All nucleotide substitutions are dimorphic. Two haplotypes fr om Thailand contain an inserted sequence encoding aspartic acid-serine-prol ine in the proline-rich region. Sequence analysis has revealed that nucleot ide diversity in PvTRAP is low although Brazilian isolates display a higher degree of variation than those from Thailand. Phylogenetic construction us ing the neighbor joining method has shown that most of the Thai and the Bra zilian isolates appear to be mainly clustered into distinct groups. Signifi cantly greater than expected values of the mean number of non-synonymous (d (n)) than synonymous (d(s)) nucleotide substitutions per site were observed in regions II and III of PvTRAP. Analysis of the published PfTRAP sequence s has shown a similar finding in regions II and IV suggesting that positive selection operates on the regions. Hence, different regions in PvTRAP and PfTRAP could be under different pressures in terms of immune selection, str uctural and/or functional constraints. (C) 2001 Elsevier Science B,V. All r ights reserved.