Cryo-EM structure of the E. coli translating ribosome in complex with SRP and its receptor - PubMed (original) (raw)

Cryo-EM structure of the E. coli translating ribosome in complex with SRP and its receptor

Leandro F Estrozi et al. Nat Struct Mol Biol. 2011 Jan.

Abstract

We report the 'early' conformation of the Escherichia coli signal recognition particle (SRP) and its receptor FtsY bound to the translating ribosome, as determined by cryo-EM. FtsY binds to the tetraloop of the SRP RNA, whereas the NG domains of the SRP protein and FtsY interact weakly in this conformation. Our results suggest that optimal positioning of the SRP RNA tetraloop and the Ffh NG domain leads to FtsY recruitment.

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Figures

Figure 1

Figure 1

Generation and Characterization of RNC-SRP-FtsY. (a) Schematic of the single-chain SRP-FtsY construct (scSRP). (b) Co-crystal structure of the Ffh (green)-FtsY (magenta) NG-domain complex,. (c) Coomassie-stained SDS-PAGE gel showing binding of the SRP (Ffh), FtsY and scSRP to RNC analyzed by ribosomal pelleting. scSRP binds in presence and absence of non-hydrolysable GTP (GMPPNP). (d) GTPase activity of the scSRP construct (dark grey) is within two-fold of unlinked SRP and FtsY (light grey) and inhibited by RNCs. Standard deviation from three different experiments is indicated by error bars. (e) Cryo-EM structure of RNC-scSRP. 30S: yellow, 50S: blue, scSRP: red, star: tunnel exit. All figures were produced with the programs Adobe Illustrator and PyMOL (

http://www.pymol.org

).

Figure 2

Figure 2

Atomic Model of the Early Conformation of scSRP. (a) View on the tunnel exit. (b) The Ffh-FtsY NG-domains have a loose interface and do not contact L23,L29. (c) FtsY G-domain contacts the RNA tetraloop (green) via Lys399, Arg402 and Lys406 (blue). View from the tunnel exit. The side-chain placement is based on the Ffh-FtsY NG-domain complex structure. (d) Ribosomal connection formed by the M-domain helices2,3 and rRNA helix24 (marine). Experimental density: grey; 4.5S RNA: orange; Ffh M-domain (helices2,3): yellow; Ffh NG-domain: limon; FtsY: magenta; rRNA: grey.

Figure 3

Figure 3

Cartoon Model of Co-translational Targeting. The Ffh N-domain binds L23 (left). Upon recognition of a signal sequence, the SRP binds with high affinity to the RNC (middle), and is prepositioned to bind FtsY. In the early conformation (right), the FtsY NG-domain contacts the 4.5S RNA tetraloop initiating the rearrangement of the GTPase domains and release of the RNC. The colored outlines are based on EM reconstructions.

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