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

• The protein translocation channel at the plastid outer envelope membrane, Toc75, is essential for the viability of plants from the embryonic stage [2].
• Finally, we employ reconstituted proteoliposomes to demonstrate that proper insertion of the receptor requires both Toc75 and Toc34 [3].
• The roles of toc34 and toc75 in targeting the toc159 preprotein receptor to chloroplasts [3].
• By contrast, atTOC75-IV is expressed uniformly throughout development and at a much lower level than atTOC75-III [4].
• The Arabidopsis (Arabidopsis thaliana) genome contains three Toc75-related sequences, termed atTOC75-I, atTOC75-III, and atTOC75-IV, which we studied using a range of molecular, genetic, and biochemical techniques [4].

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

• We evaluated their importance in the biogenesis of Toc75 by means of deletion or site-directed mutagenesis, followed by import experiments using isolated chlroplasts [5].

References