Cryo-electron microscopic structure of SecA protein bound to the 70S ribosome.
SecA is an ATP-dependent molecular motor pumping secretory and outer membrane proteins across the cytoplasmic membrane in bacteria. SecA associates with the protein-conducting channel, the heterotrimeric SecYEG complex, in a so-called posttranslational manner. A recent study further showed binding of a monomeric state of SecA to the ribosome. However, the true oligomeric state of SecA remains controversial because SecA can also form functional dimers, and high-resolution crystal structures exist for both the monomer and the dimer. Here we present the cryo-electron microscopy structures of Escherichia coli SecA bound to the ribosome. We show that not only a monomeric SecA binds to the ribosome but also that two copies of SecA can be observed that form an elongated dimer. Two copies of SecA completely surround the tunnel exit, providing a unique environment to the nascent polypeptides emerging from the ribosome. We identified the N-terminal helix of SecA required for a stable association with the ribosome. The structures indicate a possible function of the dimeric form of SecA at the ribosome.
Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany.
Rajkumar
R
Singh
Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany.
Christian
C
Kraft
Division of Structural Biology and Biochemistry, School of Biological Sciences, Nanyang Technological University, Singapore 637551.
Rahul
R
Jaiswal
Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany.
Kushal
K
Sejwal
Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany.
Vikram Babu
VB
Kasaragod
Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany.
Jochen
J
Kuper
UltraStrukturNetzwerk, Max Planck Institute for Molecular Genetics, Ihnestr. 73, 14195 Berlin, Germany; Institut für Medizinische Physik und Biophysik, Charité, Ziegelstrasse 5-8, 10117 Berlin, Germany.
Jörg
J
Bürger
UltraStrukturNetzwerk, Max Planck Institute for Molecular Genetics, Ihnestr. 73, 14195 Berlin, Germany; Institut für Medizinische Physik und Biophysik, Charité, Ziegelstrasse 5-8, 10117 Berlin, Germany.
Thorsten
T
Mielke
Department of Molecular Microbiology, Institute of Molecular Cell Biology, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands.
Joen
J
Luirink
Rudolf Virchow Center/DFG Research Center for Experimental Biomedicine, University of Würzburg, Josef Schneider Str. 2, 97078 Würzburg, Germany; Division of Structural Biology and Biochemistry, School of Biological Sciences, Nanyang Technological University, Singapore 637551. Electronic address: sbhushan@ntu.edu.sg.
Shashi
S
Bhushan
D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000648:ultrastructure*; D001426:Bacterial Proteins / Q000737:chemistry / Q000648:ultrastructure*; D003198:Computer Simulation; D020285:Cryoelectron Microscopy; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000648:ultrastructure*; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000648:ultrastructure*; D008958:Models, Molecular; D011485:Protein Binding; D017433:Protein Structure, Secondary; D054681:Ribosome Subunits, Large, Bacterial / Q000737:chemistry / Q000648:ultrastructure*; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins
70S; Cryo-EM; Electron Microscopy (EM); Protein Secretion; Protein Translocation; Ribosome; Ribosomes; SecA; SecYEG; Single Particle Analysis