Molecular cloning and expression of the VK247 circumsporozoite protein for serodiagnosis of variant form Plasmodium vivax.

Plasmodium vivax is classified into two serotypes, VK210 [the dominant form-GDRA(D/A)GQPA repeats] and VK247 [the variant form-ANGA(G/D)(N/D)QPG repeats], based on sequence variation of the repeat region of the circumsporozoite (CS) protein gene. Genomic DNA for the variant CS protein gene was obtained from field isolate strains in Myanmar. The repetitive region has highly 19 immunogenic repeats flanked by non-repeat stretches of amino acids. The sequence including this region (717 bp) was subcloned into the expression vector pQE30 and expressed in Escherichia coli. The expressed recombinant protein has a molecular weight of about 50 kDa as analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. Anti-VK247 antibodies were found in malaria patients who have been exposed to variant form of P. vivax in western blot analysis. Therefore, this recombinant protein might be a useful tool in serodiagnosis of malaria patients who have been infected with variant form of P. vivax.