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Signal sequence–independent SRP-SR complex formation at the membrane suggests an alternative targeting pathway within the SRP cycle
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...
Autores principales: | , , , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
The American Society for Cell Biology
2011
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3128533/ https://www.ncbi.nlm.nih.gov/pubmed/21551068 http://dx.doi.org/10.1091/mbc.E11-02-0152 |
Sumario: | 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. |
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