Abstract
ABSTRACTHuman DJ-1 is a highly conserved and yet functionally enigmatic protein associated with a heritable form of Parkinson’s disease. It has been suggested to be a redox-dependent regulatory scaffold, binding to proteins to modulate their function. Here we present the X-ray crystal structure of the Toxoplasma orthologue Toxoplasma gondii DJ-1 (TgDJ-1) at 2.1-Å resolution and show that it directly associates with calcium-dependent protein kinase 1 (CDPK1). The TgDJ-1 structure identifies an orthologously conserved arginine dyad that acts as a phospho-gatekeeper motif to control complex formation. We determined that the binding of TgDJ-1 to CDPK1 is sensitive to oxidation and calcium, and that this interaction potentiates CDPK1 kinase activity. Finally, we show that genetic deletion of TgDJ-1 results in upregulation of CDPK1 expression and that disruption of the CDPK1/TgDJ-1 complex in vivo prevents normal exocytosis of parasite virulence-associated organelles called micronemes. Overall, our data suggest that TgDJ-1 functions as a noncanonical kinase-regulatory scaffold that integrates multiple intracellular signals to tune microneme exocytosis in T. gondii.
Highlights
Human DJ-1 is a highly conserved and yet functionally enigmatic protein associated with a heritable form of Parkinson’s disease
We found that Toxoplasma gondii DJ-1 (TgDJ-1) Cys104 had a cysteine reactivity ratio score of 2.03, compared with the nearby reactive cysteine, cysteine 127, that is the target of WRR-086, which had a score of 3.44 (SD ϭ 0.21)
TgDJ-1 regulates the calcium-dependent protein kinase 1 (CDPK1)-mediated signaling necessary for the coordination of microneme secretion
Summary
Human DJ-1 is a highly conserved and yet functionally enigmatic protein associated with a heritable form of Parkinson’s disease. Intracellular pathogens are dependent upon their chosen host cell niche for survival Apicomplexan parasites such as Plasmodium spp. and Toxoplasma gondii utilize a complex of apical organelles consisting of dense granules, rhoptries, and micronemes, which they deploy for release (egress), attachment, and invasion of host cells, and the establishment of the parasitophorous vacuole where the parasite resides inside the host [13]. The contents of these organelles include key molecules for interacting with the host cell and, correspondingly, their secretion is tightly regulated [14]. Secretion is a calcium-driven event, which can be artificially stimulated using calcium ionophores or short-chain alcohols that trigger calcium release from internal stores [17]
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