Functional Analysis of Novel Components of the Toxoplasma Inner Membrane Complex

PROJECT SUMMARY
Toxoplasma gondii and related apicomplexan parasites contain a specialized organelle called the inner
membrane complex (IMC) that plays essential roles in host cell invasion and daughter cell formation. The IMC
consists of flattened membrane vesicles and a supporting cytoskeletal meshwork that is flanked by the plasma
membrane and subpellicular microtubules at the periphery of the parasite. Recent in vivo biotinylation (BioID)
studies have revealed a surprising level of compartmentalization within the IMC organelle, with distinct groups
of proteins segregating to the cone-shaped apical cap, the body, or to the basal complex of both the cytoskeletal
and membrane subcompartments. Analyses from our group and others have exposed new essential functions
of the IMC including the role of the apical cap complex AC9/AC10/ERK7 in mounting the conoid which is essential
for organelle secretion and invasion as well as the conserved early daughter bud protein IMC32 that is essential
for replication. In this renewal, we will expand on these studies to determine precisely how these and other critical
IMC components are able to carry out their functions. First, we will determine the role of novel apical cap proteins
that are putative interactors of the AC9/AC10/ERK7 complex and assess their role in apical cap function and
conoid assembly. We will then explore how IMC32 collaborates with the newly discovered partner IMC48 to
function at the earliest stages of parasite division and use these proteins to further explore the early daughter
bud proteome. Finally, we will exploit our recently developed photoreactive unnatural amino acid system as well
as cryo-electron tomography to determine how critical alveolins of the parasite cytoskeleton are organized to
serve as scaffolds for the organelle. Together, this project will promote a much deeper understanding of the
architecture and function of the Toxoplasma IMC. As this organelle is parasite-specific and not present in its
human host, determining precisely how these essential IMC components function promises to enable the design
of novel therapies against T. gondii and other apicomplexan parasites.

Grant Number: 5R01AI123360-09
NIH Institute/Center: NIH
Principal Investigator: Peter Bradley