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Signal sequence-independent SRP-SR complex formation at the membrane suggests an alternative targeting pathway within the SRP cycle.

Authors :
Braig D
Mircheva M
Sachelaru I
van der Sluis EO
Sturm L
Beckmann R
Koch HG
Source :
Molecular biology of the cell [Mol Biol Cell] 2011 Jul 01; Vol. 22 (13), pp. 2309-23. Date of Electronic Publication: 2011 May 05.
Publication Year :
2011

Abstract

Protein targeting by the signal recognition particle (SRP) and the bacterial SRP receptor FtsY requires a series of closely coordinated steps that monitor the presence of a substrate, the membrane, and a vacant translocon. Although the influence of substrate binding on FtsY-SRP complex formation is well documented, the contribution of the membrane is largely unknown. In the current study, we found that negatively charged phospholipids stimulate FtsY-SRP complex formation. Phospholipids act on a conserved positively charged amphipathic helix in FtsY and induce a conformational change that strongly enhances the FtsY-lipid interaction. This membrane-bound, signal sequence-independent FtsY-SRP complex is able to recruit RNCs to the membrane and to transfer them to the Sec translocon. Significantly, the same results were also observed with an artificial FtsY-SRP fusion protein, which was tethered to the membrane via a transmembrane domain. This indicates that substrate recognition by a soluble SRP is not essential for cotranslational targeting in Escherichia coli. Our findings reveal a remarkable flexibility of SRP-dependent protein targeting, as they indicate that substrate recognition can occur either in the cytosol via ribosome-bound SRP or at the membrane via a preassembled FtsY-SRP complex.

Details

Language :
English
ISSN :
1939-4586
Volume :
22
Issue :
13
Database :
MEDLINE
Journal :
Molecular biology of the cell
Publication Type :
Academic Journal
Accession number :
21551068
Full Text :
https://doi.org/10.1091/mbc.E11-02-0152