Abstract

Merozoite surface protein-1 (MSP-1) is one of the several proteins on the surface of the asexual merozoite of malaria parasites. It undergoes a two stage proteolytic cleavage to form a C-terminal 19-kDa fragment or PfMSP1₁₉ that is used for red blood cell invasion. A homologue of PfMSP-1₁₉ of Plasmodium falciparum called PvMSP-1₁₉ has been identified in Plasmodium vivax. Recently, attention has been focused on this C-terminal cysteine-rich region as an important determinant of haplotypes that characterize the malaria parasite in endemic areas. In this study, sequence specific primers were used to determine the PfMSP-1₁₉ haplotypes from field samples and PvMSP-1₁₉ haplotypes from both field and Aotus adapted parasites. 163 PfMSP-1₁₉ samples from Kisumu-Kenya were polymerase chain reaction (PCR) typed at position 1644 in the first epidermal growth factor (EGF)-like domain followed by sequencing of a random selection of positive samples so as to evaluate molecular changes at positions 1691, 1700 and 1701 in the second EGF-like domain. 121 selected samples gave bands, with 80% typing as GAA (E) and 20% as CAA (Q) at position 1644.  From computer-alignment sequences, samples 96B216 confirmed as the Uganda-PA haplotype (E-KNG), 96B209 as the PfMAD20 haplotype (E-TSR), 96B208 as the PfK1/Wellcome haplotype (Q-KNG), 96B183 as the Uganda-PA haplotype (E-KNG) and 96B017 as the E-TSG haplotype. Next, genotyping and sequence analyses of the PvMSP-1₁₉ fragment against reference sequences from GenBank demonstrated isolates as belonging to either one or the other of two parental haplotypes identified as Belem and Sal-1 strains. Comparison of PfMSP-1₁₉ and PvMSP-1₁₉ fragments demonstrated highly conserved cysteine amino acids in the two EGF-like domains.

Key words: Merozoite surface protein-1 (MSP-1), polymerase chain reaction (PCR), Plasmodium falciparum, epidermal growth factor (EGF), GenBank, Plasmodium vivax, malaria parasite.