The P25 Ookinete Surface Proteins: Homology Modeling and Phylogenetic Relationships

Sexual stages of Plasmodium such as zygote, ookinete, and young oocysts express 25 kDa surface protein P25, which along with P28 proteins protect the parasite from harmful environment inside mosquito midgut. Vaccines against these proteins induce antibodies in vertebrate host capable to inhibit parasite development in mosquito midgut and thus preventing the transmission of parasite from mosquito to other human host. Transmission-blocking vaccines help reduce malaria burden. The purpose of this study was in silico structural characterization of P25 family proteins and to predict their phylogenetic relationships with other proteins. Results indicate that members of P25 family have four EGF domains arranged in triangular fashion with major variations lying in the loop regions. All 22 cysteines are conserved forming 11 disulphide bonds. The C-loop of EGF domain IV in P25 proteins is smaller in comparison to P28 proteins. B loop of EGF domain II showed maximum RMSD variations followed by loops of EGF domain III. P25 proteins are tile-like triangular flat proteins that protect the parasite inside mosquito midgut. Obtained structures will help in understanding the biology of the parasite inside the mosquito midgut. These structures may also help in designing transmission-blocking vaccine against malaria in absence of experimentally determined structures.