ApiLoc - A database of published protein sub-cellular localisation in Apicomplexa

version 3 (curated until May 28, 2011)

Mutation of an unusual mitochondrial targeting sequence of SODB2 produces multiple targeting fates in Toxoplasma gondii.

Brydges, S. D., Carruthers, V. B. (2003 Nov 15, J Cell Sci)

Proteins destined for the mitochondria travel an intricate pathway through two membranes, each with its own receptors and channels. These proteins interact with receptors via N-terminal presequences that form amphipathic helices. Generally, these helices contain abundant positive charges on one face and hydrophobic residues on the other, but share little primary sequence homology. While extensive research on mitochondrial import has been done in yeast and mammalian cells, little is known about import or contents of the single mitochondrion of Toxoplasma gondii, a parasite in the phylum Apicomplexa. We describe here the characterization of TgSODB2, a novel, mitochondrial superoxide dismutase in T. gondii with an unusual targeting sequence consisting of a hydrophobic segment resembling a signal peptide, followed by a presequence. We show that although the hydrophobic segment is competent to target a reporter protein to the secretory system, it is prevented from directing ER translocation when coupled with the presequence. When we mutated the only charged residue in the hydrophobic sequence, ER translocation is restored and the reporter targeted to the apicoplast, a chloroplast-like organelle found in most apicomplexans. The presequence that follows is predicted to form an amphipathic helix, but targeted the cytoplasm when the hydrophobic peptide is removed. In addition to having an unusual targeting sequence, TgSODB2 is only the second mitochondrially imported, iron-containing SOD to be described.

PubMed: 14576360, full text

Localisation information

TGME49_116330 (SOD2, SODB2) iron-containing superoxide dismutase

Experimental localisation: mitochondrion during intracellular tachyzoite
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "Intracellular parasites showed colocalization of the GFP signal with MitotrackerTM staining, indicating that TgSODB2 associates with the mitochondrion. TgSODB2 did not colocalize with MitotrackerTM in the host cell mitochondria surrounding the PV, demonstrating the specificity of targeting (Fig. 4A)."
  • Microscopy type: Light
  • Microscopy method: GFP tag
  • Strain: 2F
  • Gene model mapping comments: blast from AY176062
  • Localisation record: mitochondrion during intracellular tachyzoite

TGME49_064080 (ACP) acyl carrier protein

Experimental localisation: apicoplast during intracellular tachyzoite
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "The apicoplast is delineated as a single, discrete dot of GFP fluorescence in pTgACP/GFP transfected cells (third row, four-cell stage)"
  • Microscopy type: Light
  • Microscopy method: GFP tag
  • Strain: 2F
  • Gene model mapping comments: inferred from another publication
  • Localisation record: apicoplast during intracellular tachyzoite

TGME49_110780 (GRA4) hypothetical protein

Experimental localisation: parasitophorous vacuole during intracellular tachyzoite, dense granule during intracellular tachyzoite
  • Species: Toxoplasma gondii
  • Quote inferring localisation: "When cells were stained with antibodies to GRA4, a protein known to target the dense granules and PV, extensive colocalization was seen"
  • Microscopy type: Light
  • Microscopy method: polyclonal antibody directly to protein
  • Strain: 2F
  • Gene model mapping comments: inferred from another publication
  • Localisation record: PV and dense granule during intracellular tachyzoite