Preparation, crystallization and preliminary X-ray analysis of a complex between the Plasmodium vivax sexual stage 25 kDa protein Pvs25 and a malaria transmission-blocking antibody Fab fragment

The Plasmodium vivax sexual stage 25 kDa protein Pvs25, located on the surface of the ookinete form of the parasite, is a vaccine candidate designed to elicit immunity that blocks the transmission of malaria by mosquitoes. The 2A8 murine monoclonal antibody directed against recombinant Pvs25 prevents the formation of P. vivax oocysts in mosquitoes fed in the laboratory. The complex between recombinant Pvs25 and the Fab fragment of 2A8 forms crystals that diffract X-rays to 3.5 Å. Two native data sets, A and B, have been collected from crystals of the Pvs25–Fab complex. Both crystals belong to space group P2₁, with unit-cell parameters of a = 86.3, b = 61.7, c = 142.7 Å, β = 101.7° for data set A and a = 86.8, b = 61.0, c = 149.3 Å, β = 104.3° for data set B, and contain two complex molecules per asymmetric unit. Efforts are under way to reveal the structure of the Pvs25–Fab complex by molecular replacement. The three-dimensional structure of the Pvs25–Fab complex will provide an understanding of the interaction between Pvs25 and the 2A8 antibody that inhibits ookinete development in the mosquito and should aid in the development of transmission-blocking vaccines against P. vivax malaria.