Poster

  • P001

A Golgin-Like Protein is Required for Golgi Structural Maintenance and Function in Toxoplasma gondii"s Endomembrane System

Presented in

Poster Session I

Poster topics

Authors

Camille Pearce (Storrs, CT / US), Dr. Aoife Heaslip (Storrs, CT / US)

Abstract

The Golgi complex is an essential organelle in all eukaryotic cells with important roles in secretory protein processing and trafficking. In Toxoplasma gondii, the Golgi is composed of a single stack of 4-8 flattened cisternae localized at the apical side of the nucleus. It is an essential part of the parasite"s endomembrane system, but few structural proteins have been identified with roles in Golgi architectural maintenance, positioning, or function. We recently identified an uncharacterized protein (TGME49_213392) that localizes to the Golgi. This 253kDa protein contains an N-terminal intrinsically disordered domain and C-terminal 1000 amino acid coiled-coil domain. It has therefore been named "GLCC" for Golgi-localized coiled-coil domain containing protein. To investigate the role of this protein, GLCC was endogenously tagged with a 3xTy epitope and mAID to facilitate protein depletion using the auxin inducible degron system. GLCC was found to be essential for parasite survival by plaque assay. 15 hours after GLCC depletion, Golgi length was reduced by 56.5% from 0.95±0.02µm in control parasites to 0.53±0.01µm in GLCC knockdown parasites. Transmission electron microscopy showed disorganization of the Golgi cisternae. After 48 hours of auxin treatment, GRASP had a diffuse cytosolic localization in ~50% of parasites, indicating that GLCC is essential for maintaining Golgi structure. GLCC depleted parasites showed a decrease in growth rate starting just 18 hours post GLCC knockdown and asynchronous replication of daughter parasites. 44% of knockdown parasites had an aberrant morphology having lost their canonical crescent shape. GLCC depleted parasites failed to egress naturally, even after 60 hours of growth in their host cells. Interestingly, micronemes and rhoptries, organelles thought to be formed in a Golgi dependent manner, appeared unaffected by the loss of GLCC even at late time points when Golgi integrity was compromised. GLCC knockdown did not affect calcium ionophore induced egress. This suggests there is a Golgi-independent pathway for organelle recycling and/or formation. Collectively, this study identified a protein essential for Golgi structural maintenance and the GLCC knockdown parasite line provides a tool for an in-depth characterization of Golgi function within the parasite endomembrane pathway.

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