Structure of the signal recognition particle interacting with the elongation-arrested ribosome


Cotranslational translocation of proteins across or into membranes is a vital process in all kingdoms of life. It requires that the translating ribosome be targeted to the membrane by the signal recognition particle (SRP), an evolutionarily conserved ribonucleoprotein particle. SRP recognizes signal sequences of nascent protein chains emerging from the ribosome. Subsequent binding of SRP leads to a pause in peptide elongation and to the ribosome docking to the membrane-bound SRP receptor. Here we present the structure of a targeting complex consisting of mammalian SRP bound to an active 80S ribosome carrying a signal sequence. This structure, solved to 12 Å by cryo-electron microscopy, enables us to generate a molecular model of SRP in its functional conformation. The model shows how the S domain of SRP contacts the large ribosomal subunit at the nascent chain exit site to bind the signal sequence, and that the Alu domain reaches into the elongation-factor-binding site of the ribosome, explaining its elongation arrest activity.

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Figure 1: Cryo-EM map of mammalian SRP bound to 80S RNC at 12.0 Å.
Figure 2: Molecular model of SRP.
Figure 3: Interaction of the SRP S domain with the 80S ribosome.
Figure 4: Interaction of the SRP Alu domain with the 80S ribosome.
Figure 5: Signal-sequence-dependent SRP–ribosome interaction.


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We thank C. Böttcher for help with the F20 cryo-microscope; U. Bach for technical assistance; and B. Dobberstein for support. This work was supported by a grant of the VolkswagenStiftung (to R.B.), by grants from NIH, NSF and HHMI (to J.F.) and by the European Union and the Senatsverwaltung für Wissenschaft, Forschung und Kultur Berlin in the context of the Ultra-Structure Network.

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Correspondence to Roland Beckmann.

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Supplementary information

Supplementary Figure 1

Purification of RNCs and reconstitution of the RNC-SRP complex. (JPG 43 kb)

Supplementary Figure 2

Cryo-EM map and resolution of the SRP-RNC complex. (JPG 93 kb)

Supplementary Movie 1

Animated cryo-EM structure of RNC-SRP complex as shown in Fig. 1. (MPG 3035 kb)

Supplementary Movie 2

Animated molecular model of mammalian SRP as shown in Fig. 2. (MPG 2941 kb)

Supplementary Figure and Movie Legends (DOC 20 kb)

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Halic, M., Becker, T., Pool, M. et al. Structure of the signal recognition particle interacting with the elongation-arrested ribosome. Nature 427, 808–814 (2004).

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