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Import of barley photosystem i subunit N into the thylakoid lumen is mediated by a bipartite presequence lacking an intermediate processing site: Role of the δpH in translocation across the thylakoid membrane

Import of barley photosystem i subunit N into the thylakoid lumen is mediated by a bipartite presequence lacking an intermediate processing site: Role of the δpH in translocation across the thylakoid membrane
Import of barley photosystem i subunit N into the thylakoid lumen is mediated by a bipartite presequence lacking an intermediate processing site: Role of the δpH in translocation across the thylakoid membrane

Translocation across the thylakoid membrane of the recently identified photosystem I polypeptide, PSI-N, has been analyzed in pea (Pisum sativum) and barley (Hordeum vulgare). PSI-N from barley is synthesized in the cytosol with a bipartite presequence similar in structural terms to those of other cytosolically synthesized proteins routed to the thylakoid lumen. In vitro reconstitution assays demonstrate that translocation into thylakoids is absolutely dependent on the transthylakoidal ΔpH, but that nucleotide triphosphates are not required; the translocation mechanism is thus similar in these respects to those utilized by the 23- and 16-kDa proteins of the oxygen-evolving complex. The translocation of PSI-N is unique in that the presequence of PSI-N does not contain an intermediate cleavage site for the stromal processing peptidase; import experiments using intact chloroplasts depleted of a ΔpH by nigericin treatment demonstrate the accumulation of the full precursor protein in the stroma. Translocation across the thylakoid membrane can take place in the absence of stromal factors, although the presence of stromal extracts leads to a consistent but slight enhancement of translocation efficiency. We also show that efficient translocation of the 33-kDa protein of the oxygen-evolving complex can take place in the complete absence of a ΔpH, in apparent contradiction with earlier findings; the translocation of this protein is thus similar in several respects to that of plastocyanin. The data indicate the operation of two very different types of translocation mechanism, with PSI-N exhibiting additional separate characteristics.

0021-9258
3762-3766
Nielsen, Vibeke Skovgaard
e861adce-7ecc-4dd5-8cd2-4749f7774e19
Mant, Alexandra
63319e45-deeb-45ad-a30d-e05b42052a0d
Knoetzel, Jürgen
5b9a2161-007f-4b9c-b9b7-7225c2a19e25
Møller, Birger Lindberg
3710d2e8-db6a-4a46-beab-b46fe819eba8
Robinson, Colin
678e0157-d628-44e8-83de-3591b07c673f
Nielsen, Vibeke Skovgaard
e861adce-7ecc-4dd5-8cd2-4749f7774e19
Mant, Alexandra
63319e45-deeb-45ad-a30d-e05b42052a0d
Knoetzel, Jürgen
5b9a2161-007f-4b9c-b9b7-7225c2a19e25
Møller, Birger Lindberg
3710d2e8-db6a-4a46-beab-b46fe819eba8
Robinson, Colin
678e0157-d628-44e8-83de-3591b07c673f

Nielsen, Vibeke Skovgaard, Mant, Alexandra, Knoetzel, Jürgen, Møller, Birger Lindberg and Robinson, Colin (1994) Import of barley photosystem i subunit N into the thylakoid lumen is mediated by a bipartite presequence lacking an intermediate processing site: Role of the δpH in translocation across the thylakoid membrane. The Journal of Biological Chemistry, 269 (5), 3762-3766.

Record type: Article

Abstract

Translocation across the thylakoid membrane of the recently identified photosystem I polypeptide, PSI-N, has been analyzed in pea (Pisum sativum) and barley (Hordeum vulgare). PSI-N from barley is synthesized in the cytosol with a bipartite presequence similar in structural terms to those of other cytosolically synthesized proteins routed to the thylakoid lumen. In vitro reconstitution assays demonstrate that translocation into thylakoids is absolutely dependent on the transthylakoidal ΔpH, but that nucleotide triphosphates are not required; the translocation mechanism is thus similar in these respects to those utilized by the 23- and 16-kDa proteins of the oxygen-evolving complex. The translocation of PSI-N is unique in that the presequence of PSI-N does not contain an intermediate cleavage site for the stromal processing peptidase; import experiments using intact chloroplasts depleted of a ΔpH by nigericin treatment demonstrate the accumulation of the full precursor protein in the stroma. Translocation across the thylakoid membrane can take place in the absence of stromal factors, although the presence of stromal extracts leads to a consistent but slight enhancement of translocation efficiency. We also show that efficient translocation of the 33-kDa protein of the oxygen-evolving complex can take place in the complete absence of a ΔpH, in apparent contradiction with earlier findings; the translocation of this protein is thus similar in several respects to that of plastocyanin. The data indicate the operation of two very different types of translocation mechanism, with PSI-N exhibiting additional separate characteristics.

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Published date: 4 February 1994

Identifiers

Local EPrints ID: 413711
URI: https://eprints.soton.ac.uk/id/eprint/413711
ISSN: 0021-9258
PURE UUID: 4c005625-18af-46ee-ae27-57c15ed048be
ORCID for Alexandra Mant: ORCID iD orcid.org/0000-0001-7169-209X

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Date deposited: 31 Aug 2017 16:32
Last modified: 13 Jun 2019 00:35

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Contributors

Author: Vibeke Skovgaard Nielsen
Author: Alexandra Mant ORCID iD
Author: Jürgen Knoetzel
Author: Birger Lindberg Møller
Author: Colin Robinson

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