Cloning and characterization of the merozoite surface antigen 1 gene of Plasmodium berghei

Merozoite surface antigen 1 (MSA1) is a promising candidate for vaccine dev elopment against malaria parasites. Here, we report the complete nucleotide sequence of the gene encoding the precursor to this major surface antigen of Plasmodium berghei strain ANKA using cDNA library screening and polymera se chain reaction techniques. A single open reading frame of 5,376 basepair s encoding a protein with a calculated molecular mass of 197 kD was defined . The protein contains a putative signal peptide of 19 amino acids, a membr ane anchor sequence of 18 residues, and shows two epidermal growth factor-l ike domains rich in Cys residues at the C-terminus. There are four repeat s equences of oligopeptides in the molecule: tetrapeptide (Ser-Thr-Thr-Thr), tripeptide (Pro-Thr-Pro and Pro-Ala-Ala), and dipeptide (Ser-Gly). Furtherm ore, three nine-residue stretches of a motif (Ala-Ser-Asn-Pro-Gly-Ala-Ser-A la-Ser) are located near each other. All of these repeat sequences are unex ceptionally located in the variable regions when compared with other MSA1 m olecules. The molecule displays 79% overall identity to the analogous antig en of P. yoelii yoelii strain YM, 70% to that of P. chabaudi chabaudi strai n AS, and 38% to that of P, falciparum strain Wellcome.