Cain, Peter, Holdermann, Iris, Sinning, Irmgard, Johnson, Arthur E. and Robinson, Colin (2011) Binding of chloroplast signal recognition particle to a thylakoid membrane protein substrate in aqueous solution and delineation of the cpSRP43–substrate interaction domain. Biochemical Journal, Vol.437 (No.1). pp. 149-155. doi:10.1042/BJ20110270

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Abstract

A cpSRP [chloroplast SRP (signal recognition particle)] comprising cpSRP54 and cpSRP43 subunits mediates the insertion of light-harvesting proteins into the thylakoid membrane. We dissected its interaction with a full-length membrane protein substrate in aqueous solution by insertion of site-specific photoactivatable cross-linkers into in vitro-synthesized Lhcb1 (major light-harvesting chlorophyll-binding protein of photosystem II). We show that Lhcb1 residues 166-176 cross-link specifically to the cpSRP43 subunit. Some cross-link positions within Lhcb1 are in the 'L18' peptide required for targeting of cpSRP substrates, whereas other cross-linking positions define a new targeting signal in the third transmembrane span. Lhcb1 was not found to cross-link to cpSRP54 at any position, and cross-linking to cpSRP43 is unaffected by the absence of cpSRP54. cpSRP43 thus effectively binds substrates autonomously, and its ability to independently bind an extended 20+-residue substrate region highlights a major difference with other SRP types where the SRP54 subunit binds to hydrophobic target sequences. The results also show that cpSRP43 can bind to a hydrophobic, three-membrane span, substrate in aqueous solution, presumably reflecting a role for cpSRP in the chloroplast stroma. This mode of action, and the specificity of the cpSRP43 substrate interaction, may be associated with cpSRP's unique post-translational mode of action.

Item Type:	Journal Article
Subjects:	Q Science > QK Botany
Divisions:	Faculty of Science > Life Sciences (2010- )
Library of Congress Subject Headings (LCSH):	Chloroplasts -- Physiology, Plant proteins
Journal or Publication Title:	Biochemical Journal
Publisher:	Portland Press
ISSN:	0264-6021
Official Date:	1 July 2011
Dates:	Date Event 1 July 2011 Published
Volume:	Vol.437
Number:	No.1
Page Range:	pp. 149-155
DOI:	10.1042/BJ20110270
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	Biotechnology and Biological Sciences Research Council (Great Britain) (BBSRC), National Institutes of Health (U.S.) (NIH), Robert A. Welch Foundation
Grant number:	GM26494 (NIH), BE-0017 (Robert A. Welch Foundation)

Data sourced from Thomson Reuters' Web of Knowledge

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