Transglutaminase in Plasmodium parasites: activity and putative role in oocysts and blood stages.

Transglutaminase was identified in malaria parasites by immunofluorescence microscopy using alpha-transglutaminase antiserum. Functional enzyme was demonstrated in vivo and in vitro using labeled polyamines that become incorporated into protein substrates through TGase activity. In Plasmodium falciparum intraerythrocytic parasites, transglutaminase activity was stage-dependent: it was weak in ring-forms but much stronger in trophozoites and schizonts. High levels of activity were detected in P. gallinaceum zygotes and ookinetes and in capsules of oocysts developing on mosquito midguts. Unlike most known transglutaminases, the enzymatic activity in Plasmodium was Ca(2+)-independent. Furthermore, levels of activity were similar at 37 and 26 degrees C. Parasite transglutaminase may be responsible for the modification of erythrocytic cytoskeleton in infected cells and it may facilitate the construction of oocyst capsules by cross-linking mosquito-derived basement membrane components with Plasmodium-derived proteins.