J Biol Chem. 2012 May 4. [Epub ahead of print]
The obligate intracellular parasite Toxoplasma gondii secretes a soluble phosphatidylserine decarboxylase
Gupta N, Hartmann A, Lucius R, Voelker DR.
Humboldt University, Germany;
Toxoplasma gondii is an obligate intracellular parasite capable of causing fatal infections in immunocompromised individuals and neonates. Examination of the phosphatidylserine (PtdSer) metabolism of T. gondii reveals that the parasite secretes a soluble form of PtdSer decarboxylase (TgPSD1), which preferentially decarboxylates liposomal PtdSer with an apparent K( m) of 67 μM. The specific enzyme activity increases by 3-fold during the replication of T. gondii, and soluble PSD accounts for ~20% of the total PSD, prior to the parasite egress from host cells. Extracellular T. gondii secreted ~20% of its total PSD activity at 37°C, and the intracellular Ca(++) chelator BAPTA-AM inhibited the process by 50%. Cycloheximide, Brefeldin A, ionic composition of the medium and exogenous PtdSer did not modulate the enzyme secretion, which suggests a constitutive discharge of a presynthesized pool of PSD in axenic T. gondii. TgPSD1 consists of 968 residues with a 26-amino acid hydrophobic peptide at the N-terminus, and no predicted membrane-domain. Parasites over-expressing TgPSD1-HA secreted 10-fold more activity compared to the parental strain. Exposure of apoptotic Jurkat cells to transgenic parasites demonstrated interfacial catalysis by secreted TgPSD1 that reduced host cell surface expression of PtdSer. Immuno-localization experiments revealed that TgPSD1 resides in the dense granules of T. gondii and is also found in the parasitophorous vacuole of replicating parasites. Together, these findings demonstrate novel features of the parasite enzyme since a secreted, soluble and interfacially active form of PSD has not been previously described for any organism.
PMID: 22563079 [PubMed - as supplied by publisher]