title: Glycolipozyme MPIase is essential for topology inversion of SecG during preprotein translocation.
abstract: Presecretory proteins are translocated across biological membranes through protein-conducting channels such as Sec61 (eukaryotes) and SecYEG (bacteria). SecA, a translocation ATPase, pushes preproteins out with dynamic structural changes through SecYEG. SecG, a subunit of the SecYEG channel possessing two transmembrane stretches (TMs), undergoes topology inversion coupled with SecA-dependent translocation. Recently, we characterized membrane protein integrase (MPIase), a glycolipozyme involved in not only protein integration into membranes but also preprotein translocation. We report here that SecG inversion occurs only when MPIase associates with SecYEG. We also found that MPIase modulates the dimer orientation of SecYEG. Cysteine-scanning mutagenesis mapped SecG TM 2 to a relatively hydrophilic environment. The dimer formation of SecG, crosslinked at TM 2, was not observed on SecG inversion, indicating that SecYEG undergoes a dynamic structural change during preprotein translocation.
authors.affiliation: Cryobiofrontier Research Center, Faculty of Agriculture, Iwate University, Morioka, 020-8550 Iwate, Japan.
authors.forename: Michael
authors.initials: M
authors.lastname: Moser
authors.forename: Shushi
authors.initials: S
authors.lastname: Nagamori
authors.forename: Maria
authors.initials: M
authors.lastname: Huber
authors.forename: Hajime
authors.initials: H
authors.lastname: Tokuda
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Nishiyama
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015151:Immunoblotting; D019426:Integrases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D055503:Protein Multimerization; D011498:Protein Precursors / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D000069816:SEC Translocation Channels
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; C088616:SecG protein, E coli; C078167:OMPA outer membrane proteins; D019426:Integrases