title: Distribution of the SELMA translocon in secondary plastids of red algal origin and predicted uncoupling of ubiquitin-dependent translocation from degradation.
abstract: Protein import into complex plastids of red algal origin is a multistep process including translocons of different evolutionary origins. The symbiont-derived ERAD-like machinery (SELMA), shown to be of red algal origin, is proposed to be the transport system for preprotein import across the periplastidal membrane of heterokontophytes, haptophytes, cryptophytes, and apicomplexans. In contrast to the canonical endoplasmic reticulum-associated degradation (ERAD) system, SELMA translocation is suggested to be uncoupled from proteasomal degradation. We investigated the distribution of known and newly identified SELMA components in organisms with complex plastids of red algal origin by intensive data mining, thereby defining a set of core components present in all examined organisms. These include putative pore-forming components, a ubiquitylation machinery, as well as a Cdc48 complex. Furthermore, the set of known 20S proteasomal components in the periplastidal compartment (PPC) of diatoms was expanded. These newly identified putative SELMA components, as well as proteasomal subunits, were in vivo localized as PPC proteins in the diatom Phaeodactylum tricornutum. The presented data allow us to speculate about the specific features of SELMA translocation in contrast to the canonical ERAD system, especially the uncoupling of translocation from degradation.
authors.affiliation: Laboratory for Cell Biology, Philipps-University Marburg, Marburg, Germany.
authors.forename: Simone
authors.initials: S
authors.lastname: Stork
authors.forename: Daniel
authors.initials: D
authors.lastname: Moog
authors.forename: Jude M
authors.initials: JM
authors.lastname: Przyborski
authors.forename: Ilka
authors.initials: I
authors.lastname: Wilhelmi
authors.forename: Stefan
authors.initials: S
authors.lastname: Zauner
authors.forename: Uwe G
authors.initials: UG
authors.lastname: Maier
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins / Q000378:metabolism; D017377:Diatoms / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D060746:Endoplasmic Reticulum-Associated Degradation; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D018087:Plastids / Q000201:enzymology* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D059748:Proteolysis; D000461:Rhodophyta / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*; D000074405:Valosin Containing Protein
chemical_list: D018797:Cell Cycle Proteins; D010940:Plant Proteins; D025801:Ubiquitin; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; D000074405:Valosin Containing Protein