title: The active ring-like structure of SecA revealed by electron crystallography: conformational change upon interaction with SecB.
abstract: SecA is a multifunctional protein involved in protein translocation in bacteria. The structure of SecA on membrane is dramatically altered compared with that in solution, accompanying with functional changes. We previously reported the formation of a novel ring-like structure of SecA on lipid layers, which may constitute part of the preprotein translocation channel. In the present work, two-dimensional crystallization of Escherichia coli SecA on lipid monolayers was performed to reveal the structural details of SecA on lipid layers and to investigate its function. The 2D crystals composed of ring-like structures were obtained by specific interaction between SecA and negatively charged lipid. The 2D projection map and 3D reconstruction from negative stained 2D crystals exhibited a distinct open channel-like structure of SecA, with an outer diameter of 7 nm and an inner diameter of 2 nm, providing the structural evidence for SecA importance in forming the part of the translocation channel. This pore structure is altered after transferring crystals to the SecB solution, indicating that the lipid-specific SecA structure has the SecB binding activity. The strategy developed here provides a promising technique for studying structure of SecA complex with its ligand on membrane.
authors.affiliation: Department of Biological Sciences and Biotechnology, State-Key Laboratory of Biomembranes and Membrane Biotechnology, Tsinghua University, Beijing 100084, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Chen
authors.forename: Phang C
authors.initials: PC
authors.lastname: Tai
authors.forename: Sen-Fang
authors.initials: SF
authors.lastname: Sui
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry; D008055:Lipids; D026901:Membrane Transport Proteins / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008055:Lipids; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C057842:SecB protein, Bacteria; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins