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Gene Review:

TOC34 - translocase of chloroplast 34

Arabidopsis thaliana

Synonyms: ARABIDOPSIS THALIANA TRANSLOCON AT THE OUTER ENVELOPE MEMBRANE OF CHLOROPLASTS 34, ATTOC34, MUG13.14, MUG13_14, OEP34, ...

Wallas, T.R. et al., Becker, T. et al., Hust, B. et al., Constan, D. et al., Jelic, M. et al., et al.

Reinbothe, Pollmann, Springer, James, Tichtinsky, Reinbothe,

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High impact information on ATTOC34/OEP34

The association of Toc34 to Toc75/Toc159 is GTP dependent and enhanced by preprotein interaction [1].
Toc34, like most outer membrane proteins, is synthesized in the cytosol at its mature size without a cleavable transit peptide [2].
Among them are a 16-kDa ortholog of the previously characterized outer envelope protein Oep16 (named Ptc16) and a 33-kDa protein (Ptc33) related to the GTP-binding proteins Toc33 and Toc34 of Arabidopsis [3].
Translocon at the outer envelope membrane of chloroplasts, 34 kDa (Toc34) is a GTP-binding component of the protein import apparatus within the outer envelope membrane of plastids [4].
The Arabidopsis genome encodes two homologues of Toc34, designated atToc33 and atToc34 [4].

Biological context of ATTOC34/OEP34

In contrast, despite the complete or almost complete lack of the import receptors Toc34 and Toc159, embryo development in the a tToc33/34 and atToc132/159 mutants proceeded slowly and was arrested later at the transition to the globular and the heart stage, respectively [5].
In pea, Toc34 functions as a GTP dependent receptor for preproteins, which is controlled by protein phosphorylation [6].
The highest affinity for dimerization was for the heterodimer between Toc33 and Toc34 in the absence of GTP or GDP [6].
Indeed, in spinach we could identify at least two Toc34 proteins with different substrate specificities as demonstrated by competition and antibody inhibition experiments [7].

Anatomical context of ATTOC34/OEP34

One of the components, OEP34, is an outer membrane protein and is synthesized at its mature size in the cytosol without a distinguishable chloroplast-targeting signal [8].

Other interactions of ATTOC34/OEP34

Finally, we employ reconstituted proteoliposomes to demonstrate that proper insertion of the receptor requires both Toc75 and Toc34 [9].
In the present study, we used the Arabidopsis thaliana orthologs of Toc159 and Toc34, atToc159 and atToc33, respectively, to investigate the requirements for assembly of the trimeric Toc complex [9].

References

Preprotein recognition by the Toc complex. Becker, T., Jelic, M., Vojta, A., Radunz, A., Soll, J., Schleiff, E. EMBO J. (2004) [Pubmed]
Insertion of atToc34 into the chloroplastic outer membrane is assisted by at least two proteinaceous components in the import system. Tsai, L.Y., Tu, S.L., Li, H.M. J. Biol. Chem. (1999) [Pubmed]
A role of Toc33 in the protochlorophyllide-dependent plastid import pathway of NADPH:protochlorophyllide oxidoreductase (POR) A. Reinbothe, S., Pollmann, S., Springer, A., James, R.J., Tichtinsky, G., Reinbothe, C. Plant J. (2005) [Pubmed]
An outer envelope membrane component of the plastid protein import apparatus plays an essential role in Arabidopsis. Constan, D., Patel, R., Keegstra, K., Jarvis, P. Plant J. (2004) [Pubmed]
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]
Two Toc34 homologues with different properties. Jelic, M., Soll, J., Schleiff, E. Biochemistry (2003) [Pubmed]
At least two Toc34 protein import receptors with different specificities are also present in spinach chloroplasts. Voigt, A., Jakob, M., Klösgen, R.B., Gutensohn, M. FEBS Lett. (2005) [Pubmed]
A novel chloroplastic outer membrane-targeting signal that functions at both termini of passenger polypeptides. Li, H., Chen, L.J. J. Biol. Chem. (1997) [Pubmed]
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]

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