Characterization of the subpellicular network, a filamentous membrane skeletal component in the parasite Toxoplasma gondii

Electron microscopic examination of detergent-extracted Toxoplasma tachyzoites reveals the presence of a mechanically stable cytoskeletal structure associated with the pellicle of this parasite. This structure. composed of interwoven 8-10 nm filaments, is associated with the cytoplasmic face: of the pellicle and surrounds the microtubule-based cytoskeleton. Two protein components of this network, TgIMCl and TgIMC2, were identified. Both are novel proteins, but have a resemblance to mammalian filament proteins in that they are predicted to have extended. coiled-coil domains. TgIMCl is also homologous to articulins, the major components of the membrane skeleton of algae and free-living protists. A homologue of TgIMCl in the related malaria parasite Plasmodium falciparum was also identified suggesting the presence of structurally similar membrane skeletons ill all apicomplexan parasites. We suggest that the subpellicular network. formed by TgIMCl and 2 in Toxoplasma gondii and related parasites, plays a role in the determination of cell shape and is a source of mechanical strength. (C) 2001 Elsevier Science B.V. All rights reserved.