Crystal Structure of the Translocation ATPase SecA from Thermus thermophilus Reveals a Parallel, Head-to-Head Dimer

Dmitry G. Vassylyev, Hiroyuki Mori, Marina N. Vassylyeva, Tomoya Tsukazaki, Yoshiaki Kimura, Tahir H. Tahirov, Koreaki Ito

Research output: Contribution to journalArticlepeer-review

75 Scopus citations


The mechanism of pre-protein export through the bacterial cytoplasmic membrane, in which the SecA ATPase plays a crucial role as an "energy supplier", is poorly understood. In particular, biochemical and structural studies provide contradictory data as to the oligomeric state of SecA when it is integrated into the active trans-membrane translocase. Here, we report the 2.8 Å resolution crystal structure of the Thermus thermophilus SecA protein (TtSecA). Whereas the structure of the TtSecA monomer closely resembles that from other bacteria, the oligomeric state of TtSecA is strikingly distinct. In contrast to the antiparallel (head-to-tail) dimerization reported previously for the other bacterial systems, TtSecA forms parallel (head-to-head) dimers that are reminiscent of open scissors. The dimer interface is abundant in bulky Arg and Lys side-chains from both subunits, which stack on one another to form an unusual "basic zipper" that is highly conserved, as revealed by homology modeling and sequence analysis. The basic zipper is sealed on both ends by two pairs of the salt bridges formed between the basic side-chains from the zipper and two invariant acidic residues. The organization of the dimers, in which the two pre-protein binding domains are located proximal to each other at the tip of the "scissors", might allow a concerted mode of substrate recognition while the opening/closing of the scissors might facilitate translocation.

Original languageEnglish (US)
Pages (from-to)248-258
Number of pages11
JournalJournal of Molecular Biology
Issue number3
StatePublished - Dec 1 2006


  • SecA ATPase
  • crystal structure
  • parallel dimer
  • pre-protein
  • translocation

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology


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