Comparison of the primary structure of the 25 kDa ookinete surface antigens of Plasmodium falciparum and Plasmodium gallinaceum reveal six conserved regions.

The gene encoding the 25 kDa ookinete surface antigen (Pgs25) of Plasmodium gallinaceum has been cloned using an oligonucleotide probe directed against one of the EGF-like domains of the P. falciparum 25 kDa ookinete surface antigen (Pfs25). The Pgs25 gene codes for a polypeptide of 215 amino acids, two amino residues less than Pfs25. The deduced amino acid sequence contains a putative signal sequence at the amino-terminus, four tandemly repeated EGF-like domains, and a hydrophobic region at the carboxyl-terminus. By comparing Pgs25 with Pfs25, six conserved regions, consisting of six or more amino acid residues, have been identified. Most of the conserved regions are outside EGF-like core consensus sequences. The most striking conservation is the spacing of the cysteines.