Microsporidial mitochondrial remnants

Microsporidia are obligate intracellular parasites thought not to possess classical eukaryote organelles such as mitochondria or peroxisomes. In August 22 Nature, Bryony Williams and colleagues at The Natural History Museum, London, UK, show that in the human microsporidian parasite Trachipleisophora hominis the presence of a homolog of mitochondrial heat shock protein Hsp70 (mtHsp70) suggests the presence of a mitochondria-like organelle (Nature 2002, 418:865-869).

Williams et al. cloned and sequenced the gene encoding a mtHsp70 from T. hominis and showed that the gene contained all the residues necessary for ATPase activity. Protein and mRNA encoded by the gene were expressed in the parasite's extracellular and spore stages. Immunolocalization studies using an mtHsp70-specific antibody identified between seven and 47 small discrete structures located throughout the cytoplasm. Further analysis using gold-labeled antibodies showed these structures to be about 50 x 90 nm (about a tenth the size of a classic mitochondrion) and bounded ...