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ABSTRACT: Chlamydia is an obligate intracellular bacterium that grows and replicates inside a cytoplasmic inclusion. We report that a host protein, CD59, which regulates complement function at the surfaces of uninfected cells, can be detected at the membrane of the chlamydial inclusion. This localization to the inclusion membrane was specific for CD59 and not a general feature of other glycosylphosphatidylinositol (GPI)-anchored proteins or representative cell surface proteins. Using differential permeabilization studies, we showed that CD59 is localized to the luminal but not the cytoplasmic face of the inclusion membrane, consistent with membrane association via its GPI anchor. Furthermore, CD59 was present at the inclusion even when we prevented it from associating with membrane microdomains via the GPI anchor or when we inhibited general protein transport to the cell surface, indicating that a conventional Golgi apparatus-dependent trafficking mechanism was not involved. Based on these findings, we propose that selected host proteins are trafficked to the inclusion by a Golgi apparatus-independent pathway during a Chlamydia infection.
Infection and immunity 02/2009; 77(4):1285-92. · 4.21 Impact Factor
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ABSTRACT: The C. elegans eat-3 gene encodes a mitochondrial dynamin family member homologous to Opa1 in humans and Mgm1 in yeast. We find that mutations in the C. elegans eat-3 locus cause mitochondria to fragment in agreement with the mutant phenotypes observed in yeast and mammalian cells. Electron microscopy shows that the matrices of fragmented mitochondria in eat-3 mutants are divided by inner membrane septae, suggestive of a specific defect in fusion of the mitochondrial inner membrane. In addition, we find that C. elegans eat-3 mutant animals are smaller, grow slower, and have smaller broodsizes than C. elegans mutants with defects in other mitochondrial fission and fusion proteins. Although mammalian Opa1 is antiapoptotic, mutations in the canonical C. elegans cell death genes ced-3 and ced-4 do not suppress the slow growth and small broodsize phenotypes of eat-3 mutants. Instead, the phenotypes of eat-3 mutants are consistent with defects in oxidative phosphorylation. Moreover, eat-3 mutants are hypersensitive to paraquat, which promotes damage by free radicals, and they are sensitive to loss of the mitochondrial superoxide dismutase sod-2. We conclude that free radicals contribute to the pathology of C. elegans eat-3 mutants.
PLoS Genetics 03/2008; 4(2):e1000022. · 8.69 Impact Factor
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ABSTRACT: Deletion of the Letm1 gene correlates with the occurrence of epilepsy in patients with Wolf-Hirschhorn syndrome. The Letm1 gene encodes a mitochondrial protein that is homologous to yeast Mdm38. Yeast Mdm38 is localized to the mitochondrial inner membrane where it was proposed to act as a K+/H+ antiporter or alternatively as a chaperone for selected mitochondrial inner membrane proteins. Here, we present cellular and biochemical analysis of Letm1 in mammalian cells and an analysis of a C. elegans mutant that could serve as a model for Wolf-Hirschhorn syndrome. We localized the Letm1 protein to the mitochondrial inner membrane of mammalian cells, where it exists in a 550-kDa complex. We show that Letm1 can bind to itself in vitro, raising the possibility that it can form higher order multimers in vivo. Reduced levels of Letm1 in human cells and in C. elegans lead to swellings along the lengths of mitochondria, consistent with the phenotype observed in yeast. Electron micrographs show mitochondria with swollen matrices that are less electron-dense than matrices in normal mitochondria. The opposite effect is achieved by overexpression of Letm1. Overexpression increases the electron density of the mitochondrial matrix and swelling of cristae. Our results are therefore consistent with a protein that regulates the volume of the mitochondrial matrix.
Human Molecular Genetics 10/2007; 16(17):2061-71. · 7.64 Impact Factor
