title: Novel role of calmodulin in regulating protein transport to mitochondria in a unicellular eukaryote.
abstract: Lower eukaryotes like the kinetoplastid parasites are good models to study evolution of cellular pathways during steps to eukaryogenesis. In this study, a kinetoplastid parasite, Leishmania donovani, was used to understand the process of mitochondrial translocation of a nucleus-encoded mitochondrial protein, the mitochondrial tryparedoxin peroxidase (mTXNPx). We report the presence of an N-terminal cleavable mitochondrial targeting signal (MTS) validated through deletion and grafting experiments. We also establish a novel finding of calmodulin (CaM) binding to the MTS of mTXNPx through specific residues. Mutation of CaM binding residues, keeping intact the residues involved in mitochondrial targeting and biochemical inhibition of CaM activity both in vitro and in vivo, prevented mitochondrial translocation. Through reconstituted import assays, we demonstrate obstruction of mitochondrial translocation either in the absence of CaM or Ca(2+) or in the presence of CaM inhibitors. We also demonstrate the prevention of temperature-driven mTXNPx aggregation in the presence of CaM. These findings establish the idea that CaM is required for the transport of the protein to mitochondria through maintenance of translocation competence posttranslation.
authors.affiliation: Cell Death and Differentiation Research Laboratory, National Institute of Immunology, New Delhi, India.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Aich
authors.forename: Chandrima
authors.initials: C
authors.lastname: Shaha
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002147:Calmodulin / Q000378:metabolism*; D006801:Humans; D007893:Leishmania donovani / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007898:Leishmaniasis, Visceral / Q000469:parasitology; D008928:Mitochondria / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D010544:Peroxidases / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D021382:Protein Sorting Signals; D021381:Protein Transport; D015800:Protozoan Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D021382:Protein Sorting Signals; D015800:Protozoan Proteins; D010544:Peroxidases; C110959:tryparedoxin peroxidase
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