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.
TGME49_116330 (SOD2, SODB2) iron-containing superoxide dismutaseExperimental localisation: mitochondrion during intracellular tachyzoite
TGME49_064080 (ACP) acyl carrier proteinExperimental localisation: apicoplast during intracellular tachyzoite
TGME49_110780 (GRA4) hypothetical proteinExperimental localisation: parasitophorous vacuole during intracellular tachyzoite, dense granule during intracellular tachyzoite