Toxoplasma gondii catalase

Microbodies are enzyme-containing organelles bounded by a single unit membrane and lacking DNA. The family includes peroxisomes, glyoxysomes and glycosomes. The organelles have a variety of metabolic functions, none of which is present in all members: beta-oxidation of fatty acids, the glyoxylate cycle, alcohol oxidation, and even glycolysis have been found confined within microbodies. Animal cell peroxisomes were the first members to be identified. They were so named because of their activity in peroxide metabolism, and can be identified by the presence of catalase. The biogenesis of microbodies is not well understood. The results of studies in a variety of systems, particularly in yeast, have shown that the matrix proteins are imported posttranslationally, in a folded or even oligomerized state, while a minority of the membrane proteins may be routed via the endoplasmatic reticulum (Kunau and Erdmann, 1998; Subramani, 1998; Titorenko and Rachubinski, 1998; van der Klei and Veenhuis, 1997). Two types of signal have been defined: the C-terminal PTS-1 and the N-terminal PTS-2. The first PTS-1 signal to be identified was serine-lysine-leucineCOOH. Subsequent work has demonstrated that this signal can be very degenerate, and that the precise specificity varies between species. The spectrum of possibilities includes (S/A/C/K/N)-(K/R/H/Q/N/S)-(L/F/I/Y/M) (Amery et al., 1998; Sommer et al., 1992; Waterham et al., 1997) but all combinations have not been tested. The phylum Apicomplexa includes several human and animal parasites including Toxoplasma gondii and the Plasmodium species that cause malaria. In the mammalian host, both Toxoplasma and Plasmodium multiply intracellularly, and spread from one cell to the next via invasive extracellular forms. Electron micrographs reveal an astonishing variety of organelles. At the apex of the parasites are the rhoptries and micronemes, both involved in host cell invasion; and the dense granules, which are on the secretory pathway and involved in remodelling the vacuole into a metabolically active compartment. There are also the nucleus and a non-photosynthetic chloroplast derivative, the apicoplast (Kohler et al., 1997b; McFadden et al., 1996). In addition, mitochondrial DNA is present, and the single mitochondrion shows a tubular morphology (Seeber et al., 1998). Since microbodies have been identified in nearly all eucaryotic species investigated, we were intrigued by the apparent absence of evidence for them in Apicomplexa. A literature search revealed no mention of peroxisomes in combination with any apicomplexan species. We therefore searched for evidence of peroxisomes in T. gondii. A common marker enzyme for peroxisomes is catalase, which, along with superoxide dismutase, is involved in defence against oxidative stress and oxidative metabolic by-products. 2409 Journal of Cell Science 113, 2409-2419 (2000) Printed in Great Britain © The Company of Biologists Limited 2000 JCS1127