Binding of chloroplast signal recognition particle to a thylakoid membrane protein substrate in aqueous solution and delineation of the cpSRP43-substrate interaction domain.

Journal article

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 photo-activatable 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.

Authors: Cain, P; Holdermann, I; Sinning, I; Johnson, A; Robinson, C

• Publication status: Published
• Journal: Biochemical journal
• Volume: 437
• Issue: 1
• Pages: 149-155
• Publication date: 2011-07-01
• DOI: 10.1042/bj20110270
• EISSN: 1470-8728
• ISSN: 0264-6021
• Language: English
• Keywords: Arabidopsis Proteins; Amino Acid Sequence; Molecular Sequence Data; Chloroplasts; Membrane Proteins; Signal Recognition Particle; Solutions; Plant Proteins; Protein Conformation; Arabidopsis; Protein Structure, Tertiary; Light-Harvesting Protein Complexes; Thylakoids; Binding Sites