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Toxoplasma aldolase is required for metabolism but dispensable for host-cell invasion.

ABSTRACT: Gliding motility and host-cell invasion by apicomplexan parasites depend on cell-surface adhesins that are translocated via an actin-myosin motor beneath the membrane. The current model posits that fructose-1,6-bisphosphate aldolase (ALD) provides a critical link between the cytoplasmic tails of transmembrane adhesins and the actin-myosin motor. Here we tested this model using the Toxoplasma gondii apical membrane protein 1 (TgAMA1), which binds to aldolase in vitro. TgAMA1 cytoplasmic tail mutations that disrupt ALD binding in vitro showed no correlation with host-cell invasion, indicating this interaction is not essential. Furthermore, ALD-depleted parasites were impaired when grown in glucose, yet they showed normal gliding and invasion in glucose-free medium. Depletion of ALD in the presence of glucose led to accumulation of fructose-1,6-bisphosphate, which has been associated with toxicity in other systems. Finally, TgALD knockout parasites and an ALD mutant that specifically disrupts adhesin binding in vitro also supported normal invasion when cultured in glucose-free medium. Taken together, these results suggest that ALD is primarily important for energy metabolism rather than interacting with microneme adhesins, challenging the current model for apicomplexan motility and invasion.

SUBMITTER: Shen B

PROVIDER: S-EPMC3948255 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature

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Toxoplasma aldolase is required for metabolism but dispensable for host-cell invasion.

Shen Bang B Sibley L David LD

Proceedings of the National Academy of Sciences of the United States of America 20140218 9

Gliding motility and host-cell invasion by apicomplexan parasites depend on cell-surface adhesins that are translocated via an actin-myosin motor beneath the membrane. The current model posits that fructose-1,6-bisphosphate aldolase (ALD) provides a critical link between the cytoplasmic tails of transmembrane adhesins and the actin-myosin motor. Here we tested this model using the Toxoplasma gondii apical membrane protein 1 (TgAMA1), which binds to aldolase in vitro. TgAMA1 cytoplasmic tail muta ...[more]

PMID: 24550496

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Project description:Apicomplexan parasites actively invade host cells using a mechanism predicted to be powered by a parasite actin-dependent myosin motor. In the model apicomplexan Toxoplasma gondii, inducible knockout of the actin gene, ACT1, was recently demonstrated to limit but not completely abolish invasion. This observation has led to the provocative suggestion that T. gondii possesses alternative, ACT1-independent invasion pathways. Here, we dissected the residual invasive ability of ?act1 parasites. Surprisingly, we were able to detect residual ACT1 protein in inducible ?act1 parasites as long as 5 days after ACT1 deletion. We further found that the longer ?act1 parasites were propagated after ACT1 deletion, the more severe an invasion defect was observed. Both findings are consistent with the quantity of residual ACT1 retained in ?act1 parasites being responsible for their invasive ability. Furthermore, invasion by the ?act1 parasites was also sensitive to the actin polymerization inhibitor cytochalasin D. Finally, there was no clear defect in attachment to host cells or moving junction formation by ?act1 parasites. However, ?act1 parasites often exhibited delayed entry into host cells, suggesting a defect specific to the penetration stage of invasion. Overall, our results support a model where residual ACT1 protein retained in inducible ?act1 parasites facilitates their limited invasive ability and confirm that parasite actin is essential for efficient penetration into host cells during invasion.The prevailing model for apicomplexan invasion has recently been suggested to require major revision, based on studies where core components of the invasion machinery were genetically disrupted using a Cre-Lox-based inducible knockout system. For the myosin component of the motor thought to power invasion, an alternative parasite myosin was recently demonstrated to functionally compensate for loss of the primary myosin involved in invasion. Here, we highlight a second mechanism that can account for the surprising ability of parasites to invade after genetic disruption of core invasion machinery. Specifically, residual actin protein present in inducible knockout parasites appears able to support their limited invasion of host cells. Our results have important implications for the interpretation of the apicomplexan invasion model and also highlight significant considerations when analyzing the phenotypes of inducible knockout parasites generated using Cre-Lox technology.

Dataset Information

Toxoplasma aldolase is required for metabolism but dispensable for host-cell invasion.

Publications

Toxoplasma aldolase is required for metabolism but dispensable for host-cell invasion.

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