title: Nascent chain-monitored remodeling of the Sec machinery for salinity adaptation of marine bacteria.
abstract: SecDF interacts with the SecYEG translocon in bacteria and enhances protein export in a proton-motive-force-dependent manner. Vibrio alginolyticus, a marine-estuarine bacterium, contains two SecDF paralogs, V.SecDF1 and V.SecDF2. Here, we show that the export-enhancing function of V.SecDF1 requires Na+ instead of H+, whereas V.SecDF2 is Na+-independent, presumably requiring H+. In accord with the cation-preference difference, V.SecDF2 was only expressed under limited Na+ concentrations whereas V.SecDF1 was constitutive. However, it is not the decreased concentration of Na+ per se that the bacterium senses to up-regulate the V.SecDF2 expression, because marked up-regulation of the V.SecDF2 synthesis was observed irrespective of Na+ concentrations under certain genetic/physiological conditions: (i) when the secDF1VA gene was deleted and (ii) whenever the Sec export machinery was inhibited. VemP (Vibrio export monitoring polypeptide), a secretory polypeptide encoded by the upstream ORF of secDF2VA, plays the primary role in this regulation by undergoing regulated translational elongation arrest, which leads to unfolding of the Shine-Dalgarno sequence for translation of secDF2VA. Genetic analysis of V. alginolyticus established that the VemP-mediated regulation of SecDF2 is essential for the survival of this marine bacterium in low-salinity environments. These results reveal that a class of marine bacteria exploits nascent-chain ribosome interactions to optimize their protein export pathways to propagate efficiently under different ionic environments that they face in their life cycles.
authors.affiliation: Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan;
authors.forename: Eiji
authors.initials: E
authors.lastname: Ishii
authors.affiliation: Faculty of Life Sciences, Kyoto Sangyou University, Kita-ku, Kyoto 603-8555, Japan;
authors.forename: Shinobu
authors.initials: S
authors.lastname: Chiba
authors.affiliation: Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan;
authors.forename: Narimasa
authors.initials: N
authors.lastname: Hashimoto
authors.affiliation: Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Kojima
authors.affiliation: Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Homma
authors.affiliation: Faculty of Life Sciences, Kyoto Sangyou University, Kita-ku, Kyoto 603-8555, Japan;
authors.forename: Koreaki
authors.initials: K
authors.lastname: Ito
authors.affiliation: Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan;
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Akiyama
authors.affiliation: Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan; hiromori@virus.kyoto-u.ac.jp.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Mori
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D015964:Gene Expression Regulation, Bacterial; D015151:Immunoblotting; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis; D021381:Protein Transport / Q000235:genetics; D018892:Proton-Motive Force / Q000235:genetics; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism; D054712:Salinity; D055049:Salt Tolerance / Q000235:genetics*; D012623:Seawater / Q000382:microbiology; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism; D014733:Vibrio / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D012333:RNA, Messenger; D012964:Sodium
keywords: SecD; protein export; proton-motive force; ribosome; translation arrest