title: Mitochondrial targeting of human protoporphyrinogen oxidase.
abstract: Variegate porphyria is an autosomal dominant disorder of heme metabolism resulting from a deficiency in protoporphyrinogen oxidase, an enzyme located on the inner mitochondrial membrane. This study examined the effect of three South African VP-causing mutations (H20P, R59W, R168C) on mitochondrial targeting. Only H20P did not target, and of eight protoporphyrinogen oxidase-GFP chimeric fusion proteins created, N-terminal residues 1-17 were found to be the minimal protoporphyrinogen oxidase sequence required for efficient mitochondrial targeting. Removal of this N-terminal sequence displayed mitochondrial localization, suggesting internal mitochondrial targeting signals. In addition, six constructs were engineered to assess the effect of charge and helicity on mitochondrial targeting of the protein. Of those engineered, only the PPOX20/H20P-GFP construct abolished mitochondrial targeting, presumably through disruption of the protoporphyrinogen oxidase alpha-helix. Based on our results we propose a mechanism for protoporphyrinogen oxidase targeting to the mitochondrion.
authors.affiliation: UCT Department of Medicine, Lennox Eales Porphyria Laboratories, MRC/UCT Liver Research Centre, K-Floor, Old Groote Schuur Building, University of Cape Town Medical School, Observatory, 7925, Cape Town, Western Cape, South Africa.
authors.forename: Lester M
authors.initials: LM
authors.lastname: Davids
authors.forename: Anne V
authors.initials: AV
authors.lastname: Corrigall
authors.forename: Peter N
authors.initials: PN
authors.lastname: Meissner
mesh_terms: D045744:Cell Line, Tumor; D005420:Flavoproteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008930:Mitochondria, Liver / Q000235:genetics / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008954:Models, Biological; D017354:Point Mutation; D046350:Porphyria, Variegate / Q000235:genetics; D021382:Protein Sorting Signals / Q000235:genetics; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D050768:Protoporphyrinogen Oxidase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics; D014162:Transfection
chemical_list: D005420:Flavoproteins; D024101:Mitochondrial Proteins; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; C493978:PPOX protein, human; D050768:Protoporphyrinogen Oxidase