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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

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
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

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.

0021-9258
10548-10554
Zygadlo, Agnieszka
27690761-4c43-446e-8ea2-fc2da507e512
Robinson, Colin
678e0157-d628-44e8-83de-3591b07c673f
Scheller, Henrik Vibe
a751b13f-62f4-4f71-b815-006079cacee0
Mant, Alexandra
63319e45-deeb-45ad-a30d-e05b42052a0d
Jensen, Poul Erik
6722e027-1569-4de7-88e5-94f3b1c196de
Zygadlo, Agnieszka
27690761-4c43-446e-8ea2-fc2da507e512
Robinson, Colin
678e0157-d628-44e8-83de-3591b07c673f
Scheller, Henrik Vibe
a751b13f-62f4-4f71-b815-006079cacee0
Mant, Alexandra
63319e45-deeb-45ad-a30d-e05b42052a0d
Jensen, Poul Erik
6722e027-1569-4de7-88e5-94f3b1c196de

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. The Journal of Biological Chemistry, 281 (15), 10548-10554. (doi:10.1074/jbc.M512687200).

Record type: Article

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.

Full text not available from this repository.

More information

Accepted/In Press date: 10 February 2006
e-pub ahead of print date: 14 February 2006
Published date: 14 April 2006

Identifiers

Local EPrints ID: 413713
URI: http://eprints.soton.ac.uk/id/eprint/413713
ISSN: 0021-9258
PURE UUID: 84fb0b89-9938-4905-b003-7de221bb91b1
ORCID for Alexandra Mant: ORCID iD orcid.org/0000-0001-7169-209X

Catalogue record

Date deposited: 31 Aug 2017 16:32
Last modified: 10 Sep 2019 00:45

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