|Entry||Database: EMDB / ID: EMD-10074|
|Title||SecA in complex with ribosome nascent chain|
|Sample||ribosome nascent chain in complex with SecA:|
|Method||single particle reconstruction / cryo EM / Resolution: 5.7 Å|
|Authors||Jomaa A / Shuai W / Shan S / Ban N|
|Funding support|| Switzerland, United States, 2 items |
|Citation||Journal: Nat. Struct. Mol. Biol. / Year: 2019|
Title: The molecular mechanism of cotranslational membrane protein recognition and targeting by SecA.
Authors: Shuai Wang / Ahmad Jomaa / Mateusz Jaskolowski / Chien-I Yang / Nenad Ban / Shu-Ou Shan /
Abstract: Cotranslational protein targeting is a conserved process for membrane protein biogenesis. In Escherichia coli, the essential ATPase SecA was found to cotranslationally target a subset of nascent ...Cotranslational protein targeting is a conserved process for membrane protein biogenesis. In Escherichia coli, the essential ATPase SecA was found to cotranslationally target a subset of nascent membrane proteins to the SecYEG translocase at the plasma membrane. The molecular mechanism of this pathway remains unclear. Here we use biochemical and cryoelectron microscopy analyses to show that the amino-terminal amphipathic helix of SecA and the ribosomal protein uL23 form a composite binding site for the transmembrane domain (TMD) on the nascent protein. This binding mode further enables recognition of charged residues flanking the nascent TMD and thus explains the specificity of SecA recognition. Finally, we show that membrane-embedded SecYEG promotes handover of the translating ribosome from SecA to the translocase via a concerted mechanism. Our work provides a molecular description of the SecA-mediated cotranslational targeting pathway and demonstrates an unprecedented role of the ribosome in shielding nascent TMDs.
|Structure viewer||EM map: |
Downloads & links
|File||Download / File: emd_10074.map.gz / Format: CCP4 / Size: 6.6 MB / Type: IMAGE STORED AS FLOATING POINT NUMBER (4 BYTES)|
|Projections & slices|
Images are generated by Spider.
|Voxel size||X=Y=Z: 1.39 Å|
|Symmetry||Space group: 1|
CCP4 map header:
-Entire ribosome nascent chain in complex with SecA
|Entire||Name: ribosome nascent chain in complex with SecA / Number of components: 2|
-Component #1: protein, ribosome nascent chain in complex with SecA
|Protein||Name: ribosome nascent chain in complex with SecA / Recombinant expression: No|
|Mass||Theoretical: 2.6 MDa|
-Component #2: protein, SecA
|Protein||Name: SecA / Recombinant expression: No|
|Specimen||Specimen state: Particle / Method: cryo EM|
|Sample solution||pH: 7.4|
|Vitrification||Instrument: FEI VITROBOT MARK IV / Cryogen name: OTHER / Temperature: 277 K / Humidity: 95 %|
-Electron microscopy imaging
Model: Titan Krios / Image courtesy: FEI Company
|Imaging||Microscope: FEI TITAN KRIOS|
|Electron gun||Electron source: FIELD EMISSION GUN / Accelerating voltage: 300 kV / Electron dose: 40 e/Å2 / Illumination mode: FLOOD BEAM|
|Lens||Imaging mode: BRIGHT FIELD|
|Specimen Holder||Model: OTHER|
|Camera||Detector: FEI FALCON III (4k x 4k)|
|Processing||Method: single particle reconstruction / Applied symmetry: C1 (asymmetric) / Number of projections: 37334|
|3D reconstruction||Software: RELION / Resolution: 5.7 Å / Resolution method: FSC 0.143 CUT-OFF|
-Atomic model buiding
|Modeling #1||Refinement protocol: rigid body|
Input PDB model: 5GAG
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