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SUMMARY Apicomplexan parasites are obligate intracellular pathogens that rely on actin-based motility to drive host cell invasion. Prior in vitro studies implicated aldolase in coupling actin filaments to the cytoplasmic domains of surface adhesins in the parasite. Here, we tested the essentiality of this interaction in host cell invasion. Homology modeling indicated a partial overlap of the binding surfaces between the enzyme active site and the region responsible for interaction with the microneme protein 2 cytoplasmic tail domain (MIC2t). Targeted mutagenesis delineated residues unique to each activity based on in vitro studies. Complementation of a conditional knockout (cKO) of the T. gondii aldolase gene (TgALD1) with mutants defective in either distinct function was used to test their respective roles. Our studies demonstrate aldolase is not only required for energy production, but is also essential for efficient host cell invasion based on its ability to bridge adhesin-cytoskeleton interactions in the parasite.

Na+/H+ antiporters are found in all kingdoms of life and exhibit catalysis rates that are among the fastest of all known secondary-active transporters. Here we combine ion mobility mass spectrometry and molecular dynamics simulations to study the conformational stability and lipid-binding properties of the Na+/H+ exchanger NapA from Thermus thermophilus and compare this to the prototypical antiporter NhaA from Escherichia coli and the human homologue NHA2. We find that NapA and NHA2, but not NhaA, form stable dimers and do not selectively retain membrane lipids. By comparing wild-type NapA with engineered variants, we show that the unfolding of the protein in the gas phase involves the disruption of inter-domain contacts. Lipids around the domain interface protect the native fold in the gas phase by mediating contacts between the mobile protein segments. We speculate that elevator-type antiporters such as NapA, and likely NHA2, use a subset of annular lipids as structural support to facilitate large-scale conformational changes within the membrane.

Background: New drugs active against persistent Mycobacterium tuberculosis are needed. Results: The fructose-1,6-bisphosphate aldolase (FBA-tb) is essential for growth of M. tuberculosis, is expressed by replicating and non-replicating bacilli, and displays plasminogen binding activity. Conclusion: FBA-tb is an essential TB enzyme that might also play a role in host/pathogen interactions. Significance: FBA-tb shows potential as a novel anti-TB therapeutic target.