An alternate mode of oligomerization for E. coli SecA

Sci Rep. 2017 Sep 18;7(1):11747. doi: 10.1038/s41598-017-11648-5.


SecA is the ATPase of preprotein translocase. SecA is a dimer in solution and changes in its oligomeric state may function in preprotein translocation. The SecA-N68 construct, in which the C-terminal helical domains of SecA are deleted, was used to investigate the mechanism of SecA oligomerization. SecA-N68 is in equilibrium between monomers, dimers, and tetramers. Subunit interactions in the SecA-N68 tetramer are mediated entirely by unstructured regions at its N- and C-termini: when the termini are deleted to yield SecA-N68∆NC, the construct is completely monomeric. This monomeric construct yielded crystals diffracting to 2.6 Å that were used to solve the structure of SecA-N68, including the "preprotein crosslinking domain" (PPXD) that was missing from previous E. coli SecA structures. The SecA-N68 structure was combined with small angle X-ray scattering (SAXS) data to construct a model of the SecA-N68 tetramer that is consistent with the essential roles of the extreme N- and C-termini in oligomerization. This mode of oligomerization, which depends on binding of the extreme N-terminus to the DEAD motor domains, NBD1 and NBD2, was used to model a novel parallel and flexible SecA solution dimer that agrees well with SAXS data.

Publication types

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

MeSH terms

  • Adenosine Triphosphatases / chemistry*
  • Adenosine Triphosphatases / genetics
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Crystallography, X-Ray
  • Escherichia coli / enzymology*
  • Escherichia coli / genetics
  • Protein Domains
  • Protein Multimerization*
  • Protein Structure, Quaternary
  • SEC Translocation Channels / chemistry*
  • SEC Translocation Channels / genetics
  • SecA Proteins


  • Bacterial Proteins
  • SEC Translocation Channels
  • Adenosine Triphosphatases
  • SecA Proteins