title: Inverse correlation between expression of the Wolfs Hirschhorn candidate gene Letm1 and mitochondrial volume in C. elegans and in mammalian cells.
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.
authors.affiliation: Department of Biological Chemistry, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095, USA.
authors.forename: Ayako
authors.initials: A
authors.lastname: Hasegawa
authors.forename: Alexander M
authors.initials: AM
authors.lastname: van der Bliek
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism / Q000648:ultrastructure; D024101:Mitochondrial Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D053142:Mitochondrial Size; D009154:Mutation; D014929:Wolfram Syndrome / Q000235:genetics
chemical_list: D029742:Caenorhabditis elegans Proteins; D002135:Calcium-Binding Proteins; C488528:LETM1 protein, human; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; C525524:letm-1 protein, C elegans