Identification of the Plasmodium chabaudi homologue of merozoite surface proteins 4 and 5 of Plasmodium falciparum

Previous studies of Plasmodium falciparum have identified a region of chrom osome 2 in which are clustered three genes for glycosylphosphatidylinositol (GPI)-anchored merozoite surface proteins, MSP2, MSP5, and MSP4, arranged in tandem, MSP4 and MSP5 both encode proteins 272 residues long that contai n hydrophobic signal sequences, GPI attachment signals, and a single epider mal growth factor (EGF)-like domain at their carboxyl termini, Nevertheless , the remainder of their protein coding regions are quite dissimilar, The l ocations and similar structural features of these genes suggest that they h ave arisen from a gene duplication event. Here we describe the identificati on of the syntenic region of the genome in the murine malaria parasite, Pla smodium chabaudi adami DS, Only one open reading frame is present in this r egion, and it encodes a protein with structural features reminiscent of bot h MSP4 and MSP5, including a single EGF-like domain. Accordingly, the gene has been designated PcMSP4/5, The homologue of the P. falciparum MSP2 gene could not be found in P, chabaudi; however, the amino terminus of the PcMSP 4/5 protein shows similarity to that of MSP2, The PcMSP4/5 gene encodes a p rotein with an apparent molecular mass of 36 kDa, and this protein is detec ted in mature stages of the parasite, The protein partitions in the deterge nt-enriched phase after Triton X-114 fractionation and is localized to the surfaces of trophozoites and developing and free merozoites. The PcMSP4/5 g ene is transcribed in both ring and trophozoite stages but appears to be sp liced in a stage-specific manner such that the central intron is spliced fr om the mRNA in the parasitic stage in which the protein is expressed.