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Gene Review

TOC75-III  -  protein TOC75-3

Arabidopsis thaliana

Synonyms: MAR1, MODIFIER OF ARG1 1, translocon at the outer envelope membrane of chloroplasts 75-III
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Disease relevance of TOC75-III

  • Development of the envelope translocon was initiated by recruitment of a cyanobacterial homolog of the protein-import channel Toc75, which belongs to a ubiquitous and essential family of Omp85/D15 outer membrane proteins of gram-negative bacteria that mediate biogenesis of beta-barrel proteins [1].

High impact information on TOC75-III


Biological context of TOC75-III

  • Toc75 (translocon at the outer envelope membrane of chloroplasts, 75 kD) is the protein translocation channel at the outer envelope membrane of plastids and was first identified in pea (Pisum sativum) using biochemical approaches [4].
  • A molecular-genetic study of the Arabidopsis Toc75 gene family [4].
  • Next, we show that disruption of a gene encoding plastidic SPase I (Plsp1) resulted in the accumulation of immature forms of Toc75, severe reduction of plastid internal membrane development, and a seedling lethal phenotype [2].
  • A potential mechanism for the biogenesis of Toc75 is discussed [5].
  • Remarkably, embryo development in the atToc75-III mutant, lacking the pore forming component of the translocase, was arrested extremely early at the two-cell stage [6].

Anatomical context of TOC75-III

  • Toc75 is the only protein identified so far in the outer membrane of chloroplasts or mitochondria that is synthesized as a larger precursor, preToc75, with a bipartite transit peptide [5].
  • Toc75 is a protein translocation channel in the outer envelope membrane of chloroplasts and its presence is essential for the biogenesis of the organelles [5].

Physical interactions of TOC75-III

  • Collectively these data suggest that Toc34 and Toc75 act sequentially to mediate docking and insertion of Toc159 resulting in assembly of the functional translocon [3].

Other interactions of TOC75-III

  • Unlike atToc75-III, the smaller atToc75-IV protein is not processed upon targeting to the envelope, and its insertion does not require ATP at high concentrations [4].

Analytical, diagnostic and therapeutic context of TOC75-III


  1. Evolution of the general protein import pathway of plastids (review). Reumann, S., Inoue, K., Keegstra, K. Mol. Membr. Biol. (2005) [Pubmed]
  2. Complete maturation of the plastid protein translocation channel requires a type I signal peptidase. Inoue, K., Baldwin, A.J., Shipman, R.L., Matsui, K., Theg, S.M., Ohme-Takagi, M. J. Cell Biol. (2005) [Pubmed]
  3. The roles of toc34 and toc75 in targeting the toc159 preprotein receptor to chloroplasts. Wallas, T.R., Smith, M.D., Sanchez-Nieto, S., Schnell, D.J. J. Biol. Chem. (2003) [Pubmed]
  4. A molecular-genetic study of the Arabidopsis Toc75 gene family. Baldwin, A., Wardle, A., Patel, R., Dudley, P., Park, S.K., Twell, D., Inoue, K., Jarvis, P. Plant Physiol. (2005) [Pubmed]
  5. A polyglycine stretch is necessary for proper targeting of the protein translocation channel precursor to the outer envelope membrane of chloroplasts. Inoue, K., Keegstra, K. Plant J. (2003) [Pubmed]
  6. Deletion of core components of the plastid protein import machinery causes differential arrest of embryo development in Arabidopsis thaliana. Hust, B., Gutensohn, M. Plant biology (Stuttgart, Germany) (2006) [Pubmed]
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