title: The N-terminal extension of plant mitochondrial carrier proteins is removed by two-step processing: the first cleavage is by the mitochondrial processing peptidase.
abstract: In contrast to yeast, many plants encode mitochondrial inner membrane carrier proteins with an N-terminal extension that is removed upon organelle import. Investigations using yeast and plant mitochondria models and purified general mitochondrial processing peptidase (MPP) indicate that the extension was removed in a two-step process. The first processing was carried out by MPP, while the second processing most probably occurs in the inter-membrane space by an as yet undefined peptidase, putatively a serine protease. Purified MPP from potato processed two carrier proteins to an intermediate size, this processing was sensitive to an MPP inhibitor (1,10-phenanthroline) and further, processing could be inhibited by changing arginine residues to glycine residues at a -3 arginine consensus processing site for MPP. Interestingly, yeast mitochondria only processed plant mitochondrial carrier proteins to the same intermediate size as purified plant MPP, and this intermediary processing did not occur in a temperature sensitive yeast mutant for MPP at the restrictive temperature. Incubation of carrier proteins with intact or lysed plant mitochondria under conditions designed to slow down the rate of import revealed that the MPP processed intermediate could be observed and chased to the mature form. The second processing step is inhibited by Pefabloc, suggesting it is carried out by a serine protease. A model for the processing of the N-terminal extension of plant mitochondrial carrier proteins is presented.
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Biomedical and Chemical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, WA 6009, Australia.
authors.forename: Monika W
authors.initials: MW
authors.lastname: Murcha
authors.forename: Dina
authors.initials: D
authors.lastname: Elhafez
authors.forename: A Harvey
authors.initials: AH
authors.lastname: Millar
authors.forename: James
authors.initials: J
authors.lastname: Whelan
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D016384:Consensus Sequence; D005998:Glycine / Q000378:metabolism; D008666:Metalloendopeptidases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology*; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D010618:Phenanthrolines / Q000494:pharmacology; D010940:Plant Proteins / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D011198:Solanum tuberosum / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology; D003313:Zea mays / Q000378:metabolism; D000096122:Mitochondrial Processing Peptidase
chemical_list: D002352:Carrier Proteins; D005998:Glycine; D008666:Metalloendopeptidases; D024101:Mitochondrial Proteins; D010618:Phenanthrolines; D010940:Plant Proteins; D011480:Protease Inhibitors; D029701:Saccharomyces cerevisiae Proteins; D015842:Serine Proteinase Inhibitors; D013450:Sulfones; D000096122:Mitochondrial Processing Peptidase; C002010:4-(2-aminoethyl)benzenesulfonylfluoride; C025205:1,10-phenanthroline