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Title: Polyglycine Acts as a Rejection Signal for Protein Transport at the Chloroplast Envelope

PolyGly is present in many proteins in various organisms. One example is found in a transmembrane β-barrel protein, translocon at the outer-envelope-membrane of chloroplasts 75 (Toc75). Toc75 requires its N-terminal extension (t75) for proper localization. t75 comprises signals for chloroplast import (n75) and envelope sorting (c75) in tandem. n75 and c75 are removed by stromal processing peptidase and plastidic type I signal peptidase 1, respectively. PolyGly is present within c75 and its deletion or substitution causes mistargeting of Toc75 to the stroma. Here in this study we have examined the properties of polyGly-dependent protein targeting using two soluble passenger proteins, the mature portion of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (mSS) and enhanced green fluorescent protein (EGFP). Both t75-mSS and t75-EGFP were imported into isolated chloroplasts and their n75 removed. Resultant c75-mSS was associated with the envelope at the intermembrane space, whereas c75-EGFP was partially exposed outside the envelope. Deletion of polyGly or substitution of tri-Ala for the critical tri-Gly segment within polyGly caused each passenger to be targeted to the stroma. Transient expression of t75-EGFP in Nicotiana benthamiana resulted in accumulation of c75-EGFP exposed at the surface of the chloroplast, but the majority of the EGFP passenger was foundmore » free in the cytosol with most of its c75 attachment removed. Results of circular dichroism analyses suggest that polyGly within c75 may form an extended conformation, which is disrupted by tri-Ala substitution. These data suggest that polyGly is distinct from a canonical stop-transfer sequence and acts as a rejection signal at the chloroplast inner envelope.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [2] ; ORCiD logo [1]
  1. Univ. of California, Davis, CA (United States). Dept. of Plant Sciences
  2. Nara Inst. of Science and Technology, Ikoma, Nara (Japan)
Publication Date:
Grant/Contract Number:
FG02-08ER15963; 1050602; 2003-02860
Type:
Published Article
Journal Name:
PLoS ONE
Additional Journal Information:
Journal Volume: 11; Journal Issue: 12; Journal ID: ISSN 1932-6203
Publisher:
Public Library of Science
Research Org:
Univ. of California, Davis, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; chloroplasts; chlorophyll
OSTI Identifier:
1335173
Alternate Identifier(s):
OSTI ID: 1361671

Endow, Joshua K., Rocha, Agostinho Gomes, Baldwin, Amy J., Roston, Rebecca L., Yamaguchi, Toshio, Kamikubo, Hironari, and Inoue, Kentaro. Polyglycine Acts as a Rejection Signal for Protein Transport at the Chloroplast Envelope. United States: N. p., Web. doi:10.1371/journal.pone.0167802.
Endow, Joshua K., Rocha, Agostinho Gomes, Baldwin, Amy J., Roston, Rebecca L., Yamaguchi, Toshio, Kamikubo, Hironari, & Inoue, Kentaro. Polyglycine Acts as a Rejection Signal for Protein Transport at the Chloroplast Envelope. United States. doi:10.1371/journal.pone.0167802.
Endow, Joshua K., Rocha, Agostinho Gomes, Baldwin, Amy J., Roston, Rebecca L., Yamaguchi, Toshio, Kamikubo, Hironari, and Inoue, Kentaro. 2016. "Polyglycine Acts as a Rejection Signal for Protein Transport at the Chloroplast Envelope". United States. doi:10.1371/journal.pone.0167802.
@article{osti_1335173,
title = {Polyglycine Acts as a Rejection Signal for Protein Transport at the Chloroplast Envelope},
author = {Endow, Joshua K. and Rocha, Agostinho Gomes and Baldwin, Amy J. and Roston, Rebecca L. and Yamaguchi, Toshio and Kamikubo, Hironari and Inoue, Kentaro},
abstractNote = {PolyGly is present in many proteins in various organisms. One example is found in a transmembrane β-barrel protein, translocon at the outer-envelope-membrane of chloroplasts 75 (Toc75). Toc75 requires its N-terminal extension (t75) for proper localization. t75 comprises signals for chloroplast import (n75) and envelope sorting (c75) in tandem. n75 and c75 are removed by stromal processing peptidase and plastidic type I signal peptidase 1, respectively. PolyGly is present within c75 and its deletion or substitution causes mistargeting of Toc75 to the stroma. Here in this study we have examined the properties of polyGly-dependent protein targeting using two soluble passenger proteins, the mature portion of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (mSS) and enhanced green fluorescent protein (EGFP). Both t75-mSS and t75-EGFP were imported into isolated chloroplasts and their n75 removed. Resultant c75-mSS was associated with the envelope at the intermembrane space, whereas c75-EGFP was partially exposed outside the envelope. Deletion of polyGly or substitution of tri-Ala for the critical tri-Gly segment within polyGly caused each passenger to be targeted to the stroma. Transient expression of t75-EGFP in Nicotiana benthamiana resulted in accumulation of c75-EGFP exposed at the surface of the chloroplast, but the majority of the EGFP passenger was found free in the cytosol with most of its c75 attachment removed. Results of circular dichroism analyses suggest that polyGly within c75 may form an extended conformation, which is disrupted by tri-Ala substitution. These data suggest that polyGly is distinct from a canonical stop-transfer sequence and acts as a rejection signal at the chloroplast inner envelope.},
doi = {10.1371/journal.pone.0167802},
journal = {PLoS ONE},
number = 12,
volume = 11,
place = {United States},
year = {2016},
month = {12}
}