Abstract
Membrane skeletons play an important role in the maintenance of cell shape and integrity in many cell types. In the protozoan parasite Toxoplasma gondii this function is performed by the subpellicular network, a resilient structure composed of tightly interwoven 10-nm filaments. We report here that this network is assembled at an early stage in the development of daughter parasites. The networks of immature and mature parasites differ dramatically with respect to their stability. Although in immature parasites the network is completely solubilized by detergent, the network in mature parasites is entirely detergent-resistant. Conversion of the detergent-labile to the detergent-resistant network occurs late in daughter cell development and appears to be coupled to proteolytic processing of the carboxyl terminus of TgIMC1, the major subunit of the network filaments. A single cysteine residue in the TgIMC1 carboxyl terminus was found to be essential for this processing event. The dramatic change in resistance to detergent extraction probably reflects an overall change in structural stability of the subpellicular network that accompanies maturation of daughter parasites and allows a switch from an assembly-competent but loose structure to one that is rigid and offers mechanical strength to the mature parasite.
Highlights
Membrane skeletons, composed of the plasma membrane and its organized underlying coat, are found in many cell types and are essential for mechanical strength and the maintenance of cell shape
The TgIMC1 in newly invaded parasites, on the other hand, appears to be relatively stable during the first 12 h of intracellular development but is degraded rapidly at the time the first parasite cell divisions become evident (Fig. 2). This result indicates that the proteins that make up the subpellicular network are not recycled and reused for the assembly of the daughter cells but are instead degraded during the late stages of endodyogeny
We present evidence that the membrane skeleton of T. gondii, the subpellicular network, is assembled as a labile structure early in the generation of daughter parasites and undergoes a rapid and dramatic increase in stability during the final stage of their maturation
Summary
Membrane skeletons, composed of the plasma membrane and its organized underlying coat, are found in many cell types and are essential for mechanical strength and the maintenance of cell shape. In the case of the amino-terminal HA-tagged TgIMC1, the protein is found in the subpellicular network of the growing daughter cells and mature parasites, indicating that it behaves analogous to the normal, endogenous TgIMC1.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
