Targeting of a polytopic membrane protein to the inner envelope membrane of chloroplasts in vivo involves multiple transmembrane segments

Kumiko Okawa, Hitoshi Inoue, Fumi Adachi, Katsuhiro Nakayama, Yasuko Ito-Inaba, Danny J. Schnell, Susumu Uehara, Takehito Inaba

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

Abstract

The inner envelope membrane (IEM) of the chloroplast plays crucial roles in forming an osmotic barrier and controlling metabolite exchange between the organelle and the cytosol. The IEM therefore harbours a number of membrane proteins and requires the import and integration of these nuclear-encoded proteins for its biogenesis. Recent studies have demonstrated that the transmembrane segment of single-spanning IEM proteins plays key roles in determining their IEM localization. However, few studies have focused on the molecular mechanisms by which polytopic membrane proteins are targeted to the IEM. In this study, we investigated the targeting mechanism of polytopic IEM proteins using the protein Cor413im1 as a model substrate. Cor413im1 does not utilize a soluble intermediate for its targeting to the IEM. Furthermore, we show that the putative fifth transmembrane segment of Cor413im1 is necessary for its targeting to the IEM. The C-terminal portion containing this transmembrane segment is also able to deliver Cor413im1 protein to the IEM. However, the fifth transmembrane segment of Cor413im1 itself is insufficient to target a fusion protein to the IEM. These data suggest that the targeting of polytopic membrane proteins to the chloroplast IEM in vivo involves multiple transmembrane segments and that chloroplasts have evolved a unique mechanism for the integration of polytopic proteins to the IEM.

Original languageEnglish
Article numberA2
JournalJournal of experimental botany
Volume65
Issue number18
DOIs
Publication statusPublished - 2014 Jul 10
Externally publishedYes

Keywords

  • Arabidopsis
  • Chloroplast
  • Cor413im1
  • Inner envelope membrane
  • Polytopic proteins
  • Protein targeting

ASJC Scopus subject areas

  • Physiology
  • Plant Science

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