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The properties of the positively charged loop region in PSI-G are essential for its "spontaneous" insertion into thylakoids and rapid assembly into the photosystem I complex
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Zygadlo, Agnieszka, Robinson, Colin, Scheller, Henrik Vibe, Mant, Alexandra and Jensen, Poul Erik (2006) The properties of the positively charged loop region in PSI-G are essential for its "spontaneous" insertion into thylakoids and rapid assembly into the photosystem I complex. Journal of Biological Chemistry, Volume 281 (Number 15). pp. 10548-10554. doi:10.1074/jbc.M512687200 ISSN 0021-9258.
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Official URL: http://dx.doi.org/10.1074/jbc.M512687200
Abstract
The PSI-G subunit of photosystem I (PSI) is an 11-kDa membrane protein that plays an important role in electron transport between plastocyanin and PSI and is involved in the stability of the PSI complex. Within the complex, the PSI-G subunit is bound to PSI-B and is in contact with Lhca1. PSI-G has two transmembrane spans connected by a positively charged stromal loop. The loop is inaccessible to proteases, indicating a tightly bound location within the PSI complex. Here, we have studied the insertion mechanism and assembly of PSI-G. We show that the protein inserts into thylakoids by a direct or "spontaneous" pathway that does not involve the activities of any known chloroplast protein-targeting machinery. Surprisingly, the positively charged stromal loop region plays a major role in this process. Mutagenesis or deletions within this region almost invariably lead to a marked lowering of insertion efficiency, strongly indicating a critical role for the loop in the organization of the transmembrane regions prior to or during membrane insertion. Finally, we have examined the assembly of newly inserted PSI-G into the PSI complex, since very little is known of the assembly pathway for this large multimeric complex. Interestingly, we find that inserted PSI-G can be found within the full PSI complex within the import assay time frame after insertion into thylakoids, strongly suggesting that PSI-G normally associates at the end of the assembly process. This is consistent with its location on the periphery of the complex.
Item Type: | Journal Article | ||||||||
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Subjects: | Q Science > QD Chemistry | ||||||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Life Sciences (2010- ) > Biological Sciences ( -2010) Faculty of Science, Engineering and Medicine > Science > Chemistry Faculty of Science, Engineering and Medicine > Science > Life Sciences (2010- ) |
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Journal or Publication Title: | Journal of Biological Chemistry | ||||||||
Publisher: | American Society for Biochemistry and Molecular Biology | ||||||||
ISSN: | 0021-9258 | ||||||||
Official Date: | 14 February 2006 | ||||||||
Dates: |
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Volume: | Volume 281 | ||||||||
Number: | Number 15 | ||||||||
Number of Pages: | 7 | ||||||||
Page Range: | pp. 10548-10554 | ||||||||
DOI: | 10.1074/jbc.M512687200 | ||||||||
Status: | Peer Reviewed | ||||||||
Publication Status: | Published | ||||||||
Access rights to Published version: | Restricted or Subscription Access |
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