title: Porins from plants. Molecular cloning and functional characterization of two new members of the porin family.
abstract: Porins are voltage-gated diffusion pores found in all eukaryotic kingdoms. Here we describe, for the first time, the identification and characterization of two cDNAs encoding porins from plants. Peptide sequences obtained from a 30-kDa protein of envelope membranes from pea root plastids allowed the isolation of two cDNA clones from pea and maize. On the protein level, both proteins are homologous by 58%. Sequence comparison against the Swiss-Prot sequence data base revealed a homology of about 25% to mitochondrial porins from fungi and human. Computer-aided predictions of the secondary structure of the plant porins revealed the presence of 16 antiparallel beta-strands that are also found in mitochondrial porins. Porins from non-green plastids and from the outer mitochondrial membrane were reconstituted into planar lipid bilayers. The proteins showed high pore-forming activities and similar single-channel conductances. In vitro translated porin was preferentially imported only into non-green plastids but not into chloroplasts. To our knowledge, this is the first example of selective import of a plastid protein into different types of plastids. This finding is in line with the observation that an immunoreactive 30-kDa band was only found in non-green plastids and mitochondria but not in chloroplasts. We conclude that mitochondria and non-green plastids possess homologous porin proteins, whereas chloroplasts are characterized by a different type of porin.
authors.affiliation: Julius-von-Sachs-Institut für Biowissenschaften, Universität Würzburg, Federal Republic of Germany.
authors.forename: K
authors.initials: K
authors.lastname: Fischer
authors.forename: A
authors.initials: A
authors.lastname: Weber
authors.forename: S
authors.initials: S
authors.lastname: Brink
authors.forename: B
authors.initials: B
authors.lastname: Arbinger
authors.forename: D
authors.initials: D
authors.lastname: Schünemann
authors.forename: S
authors.initials: S
authors.lastname: Borchert
authors.forename: H W
authors.initials: HW
authors.lastname: Heldt
authors.forename: B
authors.initials: B
authors.lastname: Popp
authors.forename: R
authors.initials: R
authors.lastname: Benz
authors.forename: T A
authors.initials: TA
authors.lastname: Link
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport; D015415:Biomarkers; D002451:Cell Compartmentation; D002458:Cell Fractionation; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D017343:Genes, Plant / Q000235:genetics*; D007425:Intracellular Membranes; D007473:Ion Channels / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D008051:Lipid Bilayers / Q000378:metabolism; D008928:Mitochondria; D008969:Molecular Sequence Data; D005810:Multigene Family; D018532:Pisum sativum; D010940:Plant Proteins / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D018517:Plant Roots; D018087:Plastids; D018272:Porins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D014176:Protein Biosynthesis; D017433:Protein Structure, Secondary; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D014675:Vegetables / Q000235:genetics*; D003313:Zea mays
chemical_list: D015415:Biomarkers; D018076:DNA, Complementary; D007473:Ion Channels; D008051:Lipid Bilayers; D010940:Plant Proteins; D018272:Porins; C089962:por1 protein, Zea mays; C089963:pspor1 protein, Pisum sativum