Join our online ASP Seminar Series Friday 15 May @1pm AEST, featuring Karan Singh, WEHI, presenting “The role of Ubiquitin during Toxoplasma Differentiation” and Katrina Larcher, WEHI presenting “Plasmodium falciparum GAPM proteins are required for merozoite invasion and gametocyte maturation” with co-chairs Ben Liffner, University of Adelaide and Grace Peters, University of New South Wales.
Please register online using this link for your unique passcode to join the seminar. After registering, you will receive a confirmation email containing information about joining the meeting.
Katrina Larcher joined the McCarthy lab at The Walter and Eliza Hall Institute for Medical Research in 2023 as an honours student where she continued on as a research assistant and has just now started a PhD investigating cytoskeletal structures.
Talk title: Plasmodium falciparum GAPM proteins are required for merozoite invasion and gametocyte maturation
Abstract: Plasmodium falciparum uses a highly conserved organelle to facilitate transition between different cellular niches throughout its lifecycle. The inner membrane complex acts as a scaffold for cytoskeletal components to support cell structure and anchor the actin myosin motor essential for invasion. Despite being well studied little is known about the organisation and assembly of the IMC and the function of many of its resident proteins. In this work we use a gene tagging and conditional knockout (cKO) approach, integrated with super-resolution microscopy and proteomic analyses, to determine the location and function of all three Glideosome Associated Protein(s) with Multiple membrane spans (GAPM) within the inner membrane complex. Quantitative proteomics indicated that loss of either GAPM1-3 leads to a decreased abundance of multiple IMC components, compromising the integrity of the structure. 3D Structured Illumination Microscopy of cKO gametocytes highlighted abnormal tubulin deposits due to incorrect coupling to the collapsed IMC whereas ultrastructure expansion microscopy of segmented schizonts indicated a total loss of microtubules along with abnormal rhoptry formation. This dysfunction prevented cKO merozoites from reinvading new red blood cells and gametocyte elongation. This work proposes the GAPM protein family acts as key anchors of cytoskeletal components to the inner membrane complex.
Bio:
Karan Singh is a 3rd year PhD student in the Tonkin Lab at The Walter and Eliza Hall Institute for Medical Research in Melbourne. Karan obtained his Bachelor of Technology and Master of Technology specializing in Biochemical Engineering in India. He now works to understand the ubiquitin signaling system in Toxoplasma gondii.
Title : The role of Ubiquitin during Toxoplasma Differentiation
Description:
A quarter of the global population is chronically infected with Toxoplasma gondii. Following infection, T. gondii switches from fast-growing tachyzoites which invade virtually any nucleated cell, to slow-growing bradyzoites with tropism towards muscle and central nervous system tissues. Bradyzoites are characteristic of chronic infection, impervious to clearance via the human immune system. Current therapies are not only inefficient in controlling latent parasite burden, but cause several serious side effects, necessitating the hunt for novel therapeutics targeting the chronic stage. Through a CRISPR screen, we identified an E3 ubiquitin ligase complex called the GID complex that regulates differentiation, named after the glucose-induced degradation deficient protein identified in yeast. We showed that loss of GID resulted in a loss of expression of known bradyzoite proteins, in a similar manner to loss of key regulators, suggesting a strong link of this E3 ligase in regulation of differentiation. We used mass spectrometry coupled with transcriptomics to map, for the first time, the global post-translational regulation during differentiation. We also used ubiquitomics to reveal substrates of the GID complex. Overall, this study will provide the first evidence of and the mechanism of the ubiquitin signaling system during differentiation in Toxoplasma and other apicomplexan parasites.
