IcsA, a polarly localized autotransporter with an atypical signal peptide, uses the Sec apparatus for secretion, although the Sec apparatus is circumferentially distributed

Mol Microbiol. 2003 Oct;50(1):45-60. doi: 10.1046/j.1365-2958.2003.03674.x.


Asymmetric localization of proteins is essential to many biological functions of bacteria. Shigella IcsA, an outer membrane protein, is localized to the old pole of the bacillus, where it mediates assembly of a polarized actin tail during infection of mammalian cells. Actin tail assembly provides the propulsive force for intracellular movement and intercellular dissemination. Localization of IcsA to the pole is independent of the amino-terminal signal peptide (Charles, M., Perez, M., Kobil, J.H., and Goldberg, M.B., 2001, Proc Natl Acad Sci USA 98: 9871-9876) suggesting that IcsA targeting occurs in the bacterial cytoplasm and that its secretion across the cytoplasmic membrane occurs only at the pole. Here, we characterize the mechanism by which IcsA is secreted across the cytoplasmic membrane. We present evidence that IcsA requires the SecA ATPase and the SecYEG membrane channel (translocon) for secretion. Our data suggest that YidC is not required for IcsA secretion. Furthermore, we show that polar localization of IcsA is independent of SecA. Finally, we demonstrate that while IcsA requires the SecYEG translocon for secretion, components of this apparatus are uniformly distributed within the membrane. Based on these data, we propose a model for coordinate polar targeting and secretion of IcsA at the bacterial pole.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphatases / genetics
  • Adenosine Triphosphatases / metabolism
  • Amino Acid Sequence
  • Bacterial Outer Membrane Proteins / analysis
  • Bacterial Outer Membrane Proteins / metabolism
  • Bacterial Proteins / metabolism*
  • Blotting, Western
  • Cell Membrane / metabolism
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / metabolism*
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism
  • Genes, Bacterial
  • Genes, Reporter
  • Green Fluorescent Proteins
  • Luminescent Proteins / metabolism
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism
  • Microscopy, Fluorescence
  • Molecular Sequence Data
  • Mutation
  • Protein Sorting Signals / genetics
  • Protein Transport / physiology*
  • SEC Translocation Channels
  • SecA Proteins
  • Shigella flexneri / cytology
  • Shigella flexneri / metabolism*
  • Signal Recognition Particle / genetics
  • Signal Recognition Particle / metabolism
  • Transcription Factors / chemistry
  • Transcription Factors / metabolism*


  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • Luminescent Proteins
  • Membrane Transport Proteins
  • Protein Sorting Signals
  • SEC Translocation Channels
  • Signal Recognition Particle
  • Transcription Factors
  • virG protein, Shigella flexneri
  • Green Fluorescent Proteins
  • Adenosine Triphosphatases
  • SecA Proteins