Quaternary structure of SecA in solution and bound to SecYEG probed at the single molecule level

Structure. 2011 Mar 9;19(3):430-9. doi: 10.1016/j.str.2010.12.016.


Dual-color fluorescence-burst analysis (DCFBA) was applied to measure the quaternary structure and high-affinity binding of the bacterial motor protein SecA to the protein-conducting channel SecYEG reconstituted into lipid vesicles. DCFBA is an equilibrium technique that enables the direct observation and quantification of protein-protein interactions at the single molecule level. SecA binds to SecYEG as a dimer with a nucleotide- and preprotein-dependent dissociation constant. One of the SecA protomers binds SecYEG in a salt-resistant manner, whereas binding of the second protomer is salt sensitive. Because protein translocation is salt sensitive, we conclude that the dimeric state of SecA is required for protein translocation. A structural model for the dimeric assembly of SecA while bound to SecYEG is proposed based on the crystal structures of the Thermotoga maritima SecA-SecYEG and the Escherichia coli SecA dimer.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / chemistry
  • Adenosine Triphosphatases / metabolism*
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / metabolism*
  • Dimerization
  • Escherichia coli / chemistry
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / metabolism*
  • Fluorescence
  • Membrane Proteins / chemistry
  • Membrane Proteins / metabolism*
  • Membrane Transport Proteins / chemistry
  • Membrane Transport Proteins / metabolism*
  • Models, Molecular
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Protein Structure, Quaternary
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism*
  • Protein Transport
  • Proteolipids / chemistry
  • SEC Translocation Channels
  • SecA Proteins
  • Sodium Chloride
  • Solutions
  • Thermotoga maritima / chemistry


  • Bacterial Proteins
  • Escherichia coli Proteins
  • Membrane Proteins
  • Membrane Transport Proteins
  • Protein Subunits
  • Proteolipids
  • SEC Translocation Channels
  • Solutions
  • proteoliposomes
  • Sodium Chloride
  • Adenosine Triphosphatases
  • SecA Proteins