Our lab aims to reveal fundamental molecular mechanisms underlying pathogenesis in the Apicomplexa – a collection of notorious human and animal parasites. Apicomplexan parasites are related based on similarities in their infection mechanism and include Plasmodium spp (malaria), Cryptosporidium spp (severe diarrhoea) and Toxoplasma gondii (toxoplasmosis).
We use a range of molecular and biochemical techniques to unveil essential processes that govern their behaviour and ability to thwart our body’s defences. Our aim is to find chinks in their armour to use for therapeutic advantage.
The lab has broad interests and currently focusses on the following questions:
Australia, University of Melbourne, BSc (Hons)
Australia, University of Melbourne, PhD
2012, BioPlatforms Award, Australian Society of Biochemistry and Molecular Biology
2010, Young Tall Poppy of the Year, Australian Institute of Policy and Science
2014, Executive Committee, Victorian Infection and Immunity Network
Uboldi AD, Wilde ML, McRae EA, Stewart RJ, Dagley LF, Yang L, Katris NJ, Hapuarachchi SV, Coffey MJ, Lehane AM, Botte CY, Waller RF, Webb AI, McConville MJ, Tonkin CJ. Protein kinase A negatively regulates Ca2+ signalling in Toxoplasma gondii. PLoS Biol. 2018 Sep 12;16(9):e2005642 PMID: 30208022
Khurana S#, Coffey MJ#, John A, Uboldi AD, Huynh MH, Stewart RJ, Carruthers V, Tonkin CJ*, Goddard-Borger ED*, Scott NE*. Protein O-fucosyltransferase 2-mediated O-glycosylation of the adhesin MIC2 is dispensable for Toxoplasma gondii tachyzoite infection. J Biol Chem. 2018 Dec 4. pii: jbc.RA118.005357. PMID: 30514763. *Co-corresponding authors # Equal contribution
McCoy JM, Stewart RJ, Uboldi AD, Li D, Schröder J, Scott NE, Papenfuss AT, Lehane AM, Foster LJ, Tonkin CJ. A forward genetic screen identifies a negative regulator of rapid Ca(2+)-dependent cell egress (MS1) in the intracellular parasite Toxoplasma gondii. J Biol Chem. 2017 May 5;292(18):7662-7674. PMID: 28258212
Stewart RJ, Whitehead L, Nijagal B, Sleebs BE, Lessene G, McConville MJ, Rogers KL, Tonkin CJ. Analysis of Ca2+ mediated signaling regulating Toxoplasma infectivity reveals complex relationships between key molecules. Cell Microbiol. 2017 Apr;19(4). PMID: 27781359
Uboldi AD#, McCoy JM#, Blume M, Gerlic M, Ferguson DJ, Dagley LF, Beahan CT, Stapleton DI, Gooley PR, Bacic A, Masters SL, Webb AI, McConville MJ, Tonkin CJ. Regulation of Starch Stores by a Ca2+-Dependent Protein Kinase Is Essential for Viable Cyst Development in Toxoplasma gondii. Cell Host Microbe. 2015 Dec 9;18(6):670-81. PMID: 26651943. # Equal contribution
Coffey MJ, Sleebs BE, Uboldi AD, Garnham A, Franco M, Marino ND, Panas MW, Ferguson DJ, Enciso M, O’Neill MT, Lopaticki S, Stewart RJ, Dewson G, Smyth GK, Smith BJ, Masters SL, Boothroyd JC, Boddey JA*, Tonkin CJ*. An aspartyl protease defines a novel pathway for export of Toxoplasma proteins into the host cell. Elife. 2015 Nov 18;4. pii: e10809. PMID: 26576949 * Co-corresponding authors
Williams MJ, Alonso H, Enciso M, Egarter S, Sheiner L, Meissner M, Striepen B, Smith BJ, Tonkin CJ. Two Essential Light Chains Regulate the MyoA Lever Arm To Promote Toxoplasma Gliding Motility. MBio. 2015 Sep 15;6(5):e00845-15. PMID: 26374117
Howard BL, Harvey KL, Stewart RJ, Azevedo MF, Crabb BS, Jennings IG, Sanders PR, Manallack DT, Thompson PE*, Tonkin CJ*, Gilson PR*. Identification of potent phosphodiesterase inhibitors that demonstrate cyclic nucleotide-dependent functions in apicomplexan parasites. ACS Chem Biol. 2015 Apr 17;10(4):1145-54. PMID: 25555060. *co-corresponding authors
McCoy JM, Whitehead L, van Dooren GG, Tonkin CJ. TgCDPK3 regulates calcium-dependent egress of Toxoplasma gondii from host cells. PLoS Pathog. 2012;8(12):e1003066 PMID: 23226109
Nebl T, Prieto JH, Kapp E, Smith BJ, Williams MJ, Yates JR 3rd, Cowman AF, Tonkin CJ. Quantitative in vivo analyses reveal calcium-dependent phosphorylation sites and identifies a novel component of the Toxoplasma invasion motor complex. PLoS Pathog. 2011 Sep;7(9):e1002222 PMID: 21980283
Throughout their complex lifecycles apicomplexan parasites pass between different hosts and encounter vastly different environments, triggering developmental progression and infectivity. This allows for their survival and propagation. Without their ability to sense environmental cues the life cycle of parasites is interrupted and they cannot survive.
Understanding the identity of environmental cues and the mechanisms parasites use to sense these remains one of the major gaps in our fundamental understanding of the pathogenesis across Apicomplexa. Furthermore, such signalling pathways offer a rich new source of drug and vaccine targets to prevent or treat infection.
Our current efforts in this area lie in understanding how parasites sense environmental cues to activate and switch off motility to regulate host cell invasion.
We utilise the powerful forward and reverse genetics and experimental tractability of Toxoplasma to understand the molecular basis of environmental sensing and signal transduction and how this process is conserved across apicomplexan species.
Central to signal transduction and activation of invasion is Ca2+ signalling and we continue to develop and adapt tools to probe the nature of this pathway (for example, the use of genetically encoded biosensors).
We are also interested in understanding how parasites produce the force required for motility and invasion. The actomyosin-based ‘glideosome’ drives parasite motility and consists of a myosin anchored to the parasite periphery by the glideosome associated protein (GAP) complex. The myosin is made up of an unusual ‘type XIV’ heavy chain – MyoA – bound by two light chains.
We are interested in defining how the MyoA produces force to drive motility. Here we use a combination of structural biology, parasite molecular biology and biophysics to understand how force is produced to drive apicomplexan motility and therefore provide a foundation in which to develop new drugs that prevent motility and invasion.
Acute toxoplasmosis is most often self-resolving but always results in a latent infection that persists for life in the muscle and central nervous system (CNS).
Latent Toxoplasma then acts as a reservoir for acute-stage reactivation which can cause disease in immunocompromised patients and those undergoing chemotherapy.
Latent infection in the eye is a major cause of progressive blindness through the destruction of infected retinal tissue. More recently, latent Toxoplasma infection has also been associated with several neuropsychiatric conditions including schizophrenia and Alzheimer’s disease, suggesting that chronic infection has a bigger effect on human health than previously thought. There are no known treatments to clear latent Toxoplasma in at-risk patients.
We are interested in understanding how Toxoplasma persists in the human host and furthermore, what consequences this infection has on brain health. We are focussed on defining the mechanisms used by latent Toxoplasma to manipulate host neurons and the functional importance this has on parasite survival. In particular we are interested in identifying parasite proteins that are exported into neurons and what role these proteins play in allowing long term survival in the brain. Furthermore, we aim to determine how latent forms regulate metabolism, which may aid their resistance to drugs that target acute stages.
We are also defining how latent Toxoplasma can contribute to brain dysfunction. In particular, we aim to understand how Toxoplasma affects neuronal function and how this translates into changes seen in neuropsychiatric conditions. We have collaborations with leading neuroscientists to understand how Toxoplasma can cause behavioural deficits associated with schizophrenia, determine the role that infection plays in the progression of Alzheimer’s disease and furthermore, how latent toxoplasmosis effects outcomes of traumatic brain injury.