Ribosome profiling reveals multiple roles of SecA in cotranslational protein export

Nat Commun. 2022 Jun 13;13(1):3393. doi: 10.1038/s41467-022-31061-5.


SecA, an ATPase known to posttranslationally translocate secretory proteins across the bacterial plasma membrane, also binds ribosomes, but the role of SecA's ribosome interaction has been unclear. Here, we used a combination of ribosome profiling methods to investigate the cotranslational actions of SecA. Our data reveal the widespread accumulation of large periplasmic loops of inner membrane proteins in the cytoplasm during their cotranslational translocation, which are specifically recognized and resolved by SecA in coordination with the proton motive force (PMF). Furthermore, SecA associates with 25% of secretory proteins with highly hydrophobic signal sequences at an early stage of translation and mediates their cotranslational transport. In contrast, the chaperone trigger factor (TF) delays SecA engagement on secretory proteins with weakly hydrophobic signal sequences, thus enforcing a posttranslational mode of their translocation. Our results elucidate the principles of SecA-driven cotranslational protein translocation and reveal a hierarchical network of protein export pathways in bacteria.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Escherichia coli Proteins* / metabolism
  • Protein Sorting Signals / genetics
  • Protein Transport
  • Ribosomes / genetics
  • Ribosomes / metabolism
  • SEC Translocation Channels / genetics
  • SEC Translocation Channels / metabolism
  • SecA Proteins


  • Bacterial Proteins
  • Escherichia coli Proteins
  • Protein Sorting Signals
  • SEC Translocation Channels
  • SecA Proteins