Alternative Processing of Arabidopsis Hsp70 Precursors during Protein Import into Chloroplasts

Ratnayake, R.M. Udayangani; Inoue, Hitoshi; Nonami, Hiroshi; Akita, Mitsuru

doi:10.1271/bbb.80408

Cited by 27 publications

(17 citation statements)

References 42 publications

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“…Hsp70-IAP comigrated with Toc75. Although Hsp70-IAP was [See online article for color version of this figure. ] suggested to localize in the intermembrane space of the envelope, recent data showed that it is most likely a stromal protein (Ratnayake et al, 2008). Our immunoprecipitation data ( Figure 3B) showed that stromal cpHsc70 not only coimmunoprecipitated Toc75, but also these two proteins comigrated as one band in SDS-PAGE.…”

Section: Discussionsupporting

confidence: 54%

“…Our immunoprecipitation data ( Figure 3B) showed that stromal cpHsc70 not only coimmunoprecipitated Toc75, but also these two proteins comigrated as one band in SDS-PAGE. Taken together, these data suggest that the long sought after Hsp70-IAP may be the stromal cpHsc70 (Ratnayake et al, 2008).…”

Section: Discussionmentioning

confidence: 62%

“…Its encoding gene has not been identified. A recent study further showed that the major protein recognized by SPA820 in pea chloroplasts is located in the stroma (Ratnayake et al, 2008). This result does not exclude the possibility that an intermembrane space Hsp70 recognized by SPA820 still exists, but it does highlight the possibility that some of the data showing interactions of Hsp70-IAP with precursors and the translocon might actually represent the interactions of stromal cpHsc70 with these components.…”

Section: Introductionmentioning

confidence: 91%

“…Furthermore, the Arabidopsis Hsp70 gene family has 14 members. Only two of them are localized in chloroplasts, and both have been shown to locate in the stroma (Ratnayake et al, 2008;Su and Li, 2008).…”

Section: Introductionmentioning

confidence: 99%

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Stromal Hsp70 Is Important for Protein Translocation into Pea and Arabidopsis Chloroplasts

2010

The Plant Cell

166

185

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Hsp70 family proteins function as motors driving protein translocation into mitochondria and the endoplasmic reticulum. Whether Hsp70 is involved in protein import into chloroplasts has not been resolved. We show here Arabidopsis thaliana knockout mutants of either of the two stromal cpHsc70s, cpHsc70-1 and cpHsc70-2, are defective in protein import into chloroplasts during early developmental stages. Protein import was found to be affected at the step of precursor translocation across the envelope membranes. From solubilized envelope membranes, stromal cpHsc70 was specifically coimmunoprecipitated with importing precursors and stoichiometric amounts of Tic110 and Hsp93. Moreover, in contrast with receptors at the outer envelope membrane, cpHsp70 is important for the import of both photosynthetic and nonphotosynthetic proteins. These data indicate that cpHsc70 is part of the chloroplast translocon for general import and is important for driving translocation into the stroma. We further analyzed the relationship of cpHsc70 with the other suggested motor system, Hsp93/Tic40. Chloroplasts from the cphsc70-1 hsp93-V double mutant had a more severe import defect than did the single mutants, suggesting that the two proteins function in parallel. The cphsc70-1 tic40 double knockout was lethal, further indicating that cpHsc70-1 and Tic40 have an overlapping essential function. In conclusion, our data indicate that chloroplasts have two chaperone systems facilitating protein translocation into the stroma: the cpHsc70 system and the Hsp93/Tic40 system.

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Section: Discussionsupporting

confidence: 54%

Section: Discussionmentioning

confidence: 62%

Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

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Stromal Hsp70 Is Important for Protein Translocation into Pea and Arabidopsis Chloroplasts

2010

The Plant Cell

166

185

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“…9) On the other hand, the in vitro protein transport assay has a longer history of use in determining not only the subcellular localization of proteins, but also suborganellar localization in chloroplasts. [10][11][12][13][14][15][16][17][18][19] In addition, various translocon components embedded in both envelope membranes, most of which have only one or two TMDs, have been determined as to their localization by this system. [20][21][22][23][24][25][26] However, because proteins with multiple TMDs are difficult to synthesize in vitro, this system is not frequently used for other proteins, with a few exceptions.…”

mentioning

confidence: 99%