A Novel Dimer Interface and Conformational Changes Revealed by an X-ray Structure of B. subtilis SecA

Jochen Zimmer, Weikai Li, Tom A. Rapoport

Research output: Contribution to journalArticlepeer-review

72 Scopus citations


The SecA ATPase moves polypeptides post-translationally across the plasma membrane of eubacteria, but the mechanism of transport is still unclear. We describe the crystal structure of a novel dimeric form of Bacillus subtilis SecA. Dimerization of SecA occurs at the prominent groove formed by the nucleotide binding domain 2 (nbd2) and the preprotein cross-linking (ppx) domain. The dimer interface is very large, burying approximately 5400 Å2 of solvent accessible surface per monomer. Single cysteine disulfide cross-linking shows the presence of this novel SecA dimer in solution. In addition, other dimers also exist in solution, arguing that they all are in equilibrium with monomeric SecA and supporting the idea that the monomer may be the functional species. Dimerization of SecA causes an α-helix of one subunit to convert to a short β-strand that participates in β-sheet formation with strands in the other subunit. This conversion of secondary structure elements occurs close to the connection between the nbd1 and ppx domains, a potential site of interaction with translocation substrate. Comparing the different X-ray structures of B. subtilis SecA suggests that small changes in the nucleotide binding domains could be amplified via helix 1 of the helical scaffold domain (hsd) to generate larger movements of the domains involved in polypeptide binding.

Original languageEnglish
Pages (from-to)259-265
Number of pages7
JournalJournal of Molecular Biology
Issue number3
StatePublished - Dec 1 2006


  • SecA
  • X-ray structure
  • protein translocation
  • signal peptide binding


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