Insertion of atToc34 into the chloroplastic outer membrane is assisted by at least two proteinaceous components in the import system

Toc34 is a member of the outer membrane translocon complex that mediates the initial stage of protein import into chloroplasts. Toc34, like most outer membrane proteins, is synthesized in the cytosol at its mature size without a cleavable transit peptide. The majority of outer membrane proteins do n...

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Bibliographic Details
Published in:The Journal of biological chemistry 1999-06, Vol.274 (26), p.18735-18740
Main Authors: Tsai, L.Y, Tu, S.L, Li, H.M
Format: Article
Language:English
Subjects:
adenosine triphosphate
Adenosine Triphosphate - metabolism
adenosinetriphosphatase
Apyrase - metabolism
Arabidopsis
Arabidopsis Proteins
Arabidopsis thaliana
binding proteins
cell membranes
chloroplasts
Chloroplasts - metabolism
guanosine triphosphate
Guanosine Triphosphate - metabolism
Membrane Proteins - metabolism
outer membrane translocon complex
Pisum sativum
Plant Proteins - metabolism
protein insertion
protein transport
Thermolysin - metabolism
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Summary:Toc34 is a member of the outer membrane translocon complex that mediates the initial stage of protein import into chloroplasts. Toc34, like most outer membrane proteins, is synthesized in the cytosol at its mature size without a cleavable transit peptide. The majority of outer membrane proteins do not require thermolysin-sensitive components on the chloroplastic surface or ATP for their insertion into the outer membrane. However, different results have been obtained concerning the factors required for Toc34 insertion into the outer membrane. Using an Arabidopsis homologue of pea Toc34, atToc34, we show that the insertion of atToc34 was greatly reduced by thermolysin pretreatment of chloroplasts as assayed either by protease digestion or by alkaline extraction. The insertion was also dependent on the presence of ATP or GTP. A mutant of atToc34 with the GTP-binding domain deleted still required ATP for optimal insertion, indicating that ATP was used by other protein components in the import system. The ATP-supported insertion was observed even in thermolysin-pretreated chloroplasts, suggesting that the protein component responsible for ATP-stimulated insertion is a different protein from the thermolysin-sensitive component that assists atToc34 insertion.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.274.26.18735