Press Releases
May 12, 2011

First elucidation of the mechanism of cation-dependent protein export from the cell.

  • Osamu Nureki (Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo)
  • Koreaki Ito (Kyoto Sangyo University)
  • Tomoya Tsukazaki (Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo)
  • Hiroyuki Mori (Institute for Virus Research, Kyoto University)


Transport of proteins across membranes is one of the fundamental and essential cellular activities in all organisms. We solved the first 3D structure of a membrane component SecDF, which plays an important role in efficient translocation of newly synthesized proteins across the membrane in bacteria. From the structural features and functional analyses, we proposed that SecDF functions as a membrane-integrated chaperone, which drives movement of proteins without using a major currency, ATP, of energy, but with remarkable cycles of conformational changes, powered by a proton (H+ ion) gradient across the membrane. Our model of the SecDF function has been verified by a series of biochemical and biophysical approaches. This research uncovers a new, atomic-level principle that underlies the cellular protein delivery systems in particular and biological mechanisms of active transport in general, by which cells acquire or dispose not only macromolecules but also ions, drugs and nutrients. This study was published in Nature online on May 12th (Japan time).

Paper information

Tomoya Tsukazaki, Hiroyuki Mori, Yuka Echizen, Ryuichiro Ishitani, Shuya Fukai, Takeshi Tanaka, Anna Perederina, Dmitry G. Vassylyev, Toshiyuki Kohno, Andrés D. Maturana, Koreaki Ito and Osamu Nureki, “Structure and function of a membrane component SecDF that enhances protein export”
Nature, published online on 12 May, 2011.

Figure 1

Figure 1. Protein translocation and structure of SecDF. A, Sec protein translocation. B, Crystal structure of SecDF. SecDF consists of a pseudo-symmetrical 12-helix transmembrane domain (TM) and two protruding periplasmic domains.

Figure 2

Figure 2. F form and I form of SecDF.

Figure 3

Figure 3. Functionally important, conserved residues in the TM regions The TMs are numbered.

Figure 4

Figure 4. Working model of the PMF-driven protein translocation by SecDF. A, F form, preprotein-capturing state. B, I form, preprotein-holding state. C, I to F transition and preprotein-releasing state. The two essential charged residues of SecDF are highlighted. SecYEG, grey; SecA, green; preprotein, black line; proton movement, white arrow.