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

Electron microscopic examination of detergent-extracted Toxoplasma tachyzoi tes reveals the presence of a mechanically stable cytoskeletal structure as sociated with the pellicle of this parasite. This structure. composed of in terwoven 8-10 nm filaments, is associated with the cytoplasmic face: of the pellicle and surrounds the microtubule-based cytoskeleton. Two protein com ponents of this network, TgIMCl and TgIMC2, were identified. Both are novel proteins, but have a resemblance to mammalian filament proteins in that th ey are predicted to have extended. coiled-coil domains. TgIMCl is also homo logous to articulins, the major components of the membrane skeleton of alga e and free-living protists. A homologue of TgIMCl in the related malaria pa rasite 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 Toxoplas ma 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.