Characterization of atypical BAR domain-containing proteins coded byToxoplasma gondii

Abstract

Toxoplasma gondii, the causative agent of toxoplasmosis, infects cells and replicates insideviathe secretion of factors stored in specialized organelles (rhoptries, micronemes, dense granules) and the capture of host materials. The genesis of the secretory organelles and the processes of secretion and endocytosis depend on vesicular trafficking events whose molecular bases remain poorly known. Notably, there is no characterization of the BAR (Bin/Amphiphysin/Rvs) domain-containing proteins expressed byT. gondiiand other apicomplexans, although such proteins are known to play critical roles in vesicular trafficking in other eukaryotes. Here, by combining structural analyses within vitroassays and cellular observations, we have characterizedTgREMIND (REgulators of Membrane Interacting Domains), involved in the genesis of rhoptries and dense granules, andTgBAR2 found at the parasite cortex. We establish thatTgREMIND comprises an F-BAR domain that can bind curved neutral membranes with no strict phosphoinositide requirement and exert a membrane remodeling activity. Next, we establish thatTgREMIND contains a new structural domain called REMIND, which negatively regulates the membrane-binding capacities of the F-BAR domain. In parallel, we report thatTgBAR2 contains a BAR domain with an extremely basic membrane-binding interface able to deform anionic membranes into very narrow tubules. Our data show thatT. gondiicodes for two atypical BAR domain-containing proteins with very contrasting membrane-binding properties, allowing them to function in two distinct regions of the parasite trafficking system.