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Distinct 'assisted' and 'spontaneous' mechanisms for the insertion of polytopic chlorophyll-binding proteins into the thylakoid membrane

Distinct 'assisted' and 'spontaneous' mechanisms for the insertion of polytopic chlorophyll-binding proteins into the thylakoid membrane
Distinct 'assisted' and 'spontaneous' mechanisms for the insertion of polytopic chlorophyll-binding proteins into the thylakoid membrane

The biogenesis of several bacterial polytopic membrane proteins has been shown to require signal recognition particle (SRP) and protein transport machinery, and one such protein, the major light-harvesting chlorophyll- binding protein (LHCP) exhibits these requirements in chloroplasts. In this report we have used in vitro insertion assays to analyze four additional members of the chlorophyll-a/b-binding protein family. We show that two members, Lhca1 and Lhcb5, display an absolute requirement for stroma, nucleoside triphosphates, and protein transport apparatus, indicating an 'assisted' pathway that probably resembles that of LHCP. Two other members, however, namely an early light-inducible protein 2 (Elip2) and photosystem II subunit S (PsbS), can insert efficiently in the complete absence of SRP, SecA activity, nucleoside triphosphates, or a functional Sec system. The data suggest a possibly spontaneous insertion mechanism that, to date, has been characterized only for simple single-span proteins. Of the membrane proteins whose insertion into thylakoids has been analyzed, five have now been shown to insert by a SRP/Sec-independent mechanism, suggesting that this is a mainstream form of targeting pathway. We also show that PsbS and Elip2 molecules are capable of following either 'unassisted' or assisted pathways, and we discuss the implications for the mechanism and role of SRP in chloroplasts.

0021-9258
4715-4721
Kim, Soo Jung
39c39977-8bfe-4894-bd72-c955b5ebb523
Jansson, Stefan
1796ac57-d64d-43dd-97b7-7700ce349c27
Hoffman, Neil E.
02af8ad8-e909-4bb7-9ae9-842281818bd0
Robinson, Colin
678e0157-d628-44e8-83de-3591b07c673f
Mant, Alexandra
63319e45-deeb-45ad-a30d-e05b42052a0d
Kim, Soo Jung
39c39977-8bfe-4894-bd72-c955b5ebb523
Jansson, Stefan
1796ac57-d64d-43dd-97b7-7700ce349c27
Hoffman, Neil E.
02af8ad8-e909-4bb7-9ae9-842281818bd0
Robinson, Colin
678e0157-d628-44e8-83de-3591b07c673f
Mant, Alexandra
63319e45-deeb-45ad-a30d-e05b42052a0d

Kim, Soo Jung, Jansson, Stefan, Hoffman, Neil E., Robinson, Colin and Mant, Alexandra (1999) Distinct 'assisted' and 'spontaneous' mechanisms for the insertion of polytopic chlorophyll-binding proteins into the thylakoid membrane. The Journal of Biological Chemistry, 274 (8), 4715-4721. (doi:10.1074/jbc.274.8.4715).

Record type: Article

Abstract

The biogenesis of several bacterial polytopic membrane proteins has been shown to require signal recognition particle (SRP) and protein transport machinery, and one such protein, the major light-harvesting chlorophyll- binding protein (LHCP) exhibits these requirements in chloroplasts. In this report we have used in vitro insertion assays to analyze four additional members of the chlorophyll-a/b-binding protein family. We show that two members, Lhca1 and Lhcb5, display an absolute requirement for stroma, nucleoside triphosphates, and protein transport apparatus, indicating an 'assisted' pathway that probably resembles that of LHCP. Two other members, however, namely an early light-inducible protein 2 (Elip2) and photosystem II subunit S (PsbS), can insert efficiently in the complete absence of SRP, SecA activity, nucleoside triphosphates, or a functional Sec system. The data suggest a possibly spontaneous insertion mechanism that, to date, has been characterized only for simple single-span proteins. Of the membrane proteins whose insertion into thylakoids has been analyzed, five have now been shown to insert by a SRP/Sec-independent mechanism, suggesting that this is a mainstream form of targeting pathway. We also show that PsbS and Elip2 molecules are capable of following either 'unassisted' or assisted pathways, and we discuss the implications for the mechanism and role of SRP in chloroplasts.

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Published date: 19 February 1999

Identifiers

Local EPrints ID: 413069
URI: http://eprints.soton.ac.uk/id/eprint/413069
ISSN: 0021-9258
PURE UUID: 80562dac-e24c-4d71-ba19-55ef993731c6
ORCID for Alexandra Mant: ORCID iD orcid.org/0000-0001-7169-209X

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Date deposited: 14 Aug 2017 16:31
Last modified: 07 Oct 2020 01:50

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Contributors

Author: Soo Jung Kim
Author: Stefan Jansson
Author: Neil E. Hoffman
Author: Colin Robinson
Author: Alexandra Mant ORCID iD

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