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Nat Commun. 2019 Jun 28;10(1):2872. doi: 10.1038/s41467-019-10918-2.

Structure of the substrate-engaged SecA-SecY protein translocation machine.

Author information

1
State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China.
2
University of California-Berkeley, Stanley Hall, Berkeley, CA, 94720, USA.
3
Department of Cell Biology, Howard Hughes Medical Institute and Harvard Medical School, 240 Longwood Avenue, Boston, MA, 02115, USA.
4
Department of Cell Biology, Howard Hughes Medical Institute and Harvard Medical School, 240 Longwood Avenue, Boston, MA, 02115, USA. tom_rapoport@hms.harvard.edu.
5
State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China. gaon@pku.edu.cn.
6
State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China. long_li@pku.edu.cn.

Abstract

The Sec61/SecY channel allows the translocation of many proteins across the eukaryotic endoplasmic reticulum membrane or the prokaryotic plasma membrane. In bacteria, most secretory proteins are transported post-translationally through the SecY channel by the SecA ATPase. How a polypeptide is moved through the SecA-SecY complex is poorly understood, as structural information is lacking. Here, we report an electron cryo-microscopy (cryo-EM) structure of a translocating SecA-SecY complex in a lipid environment. The translocating polypeptide chain can be traced through both SecA and SecY. In the captured transition state of ATP hydrolysis, SecA's two-helix finger is close to the polypeptide, while SecA's clamp interacts with the polypeptide in a sequence-independent manner by inducing a short β-strand. Taking into account previous biochemical and biophysical data, our structure is consistent with a model in which the two-helix finger and clamp cooperate during the ATPase cycle to move a polypeptide through the channel.

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