The SecYEG preprotein translocation channel is a conformationally dynamic and dimeric structure.
Escherichia coli preprotein translocase comprises a membrane-embedded trimeric complex of SecY, SecE and SecG. Previous studies have shown that this complex forms ring-like assemblies, which are thought to represent the preprotein translocation channel across the membrane. We have analyzed the functional state and the quaternary structure of the SecYEG translocase by employing cross-linking and blue native gel electrophoresis. The results show that the SecYEG monomer is a highly dynamic structure, spontaneously and reversibly associating into dimers. SecG-dependent tetramers and higher order SecYEG multimers can also exist in the membrane, but these structures form at high SecYEG concentration or upon overproduction of the complex only. The translocation process does not affect the oligomeric state of the translocase and arrested preproteins can be trapped with SecYEG or SecYE dimers. Dissociation of the dimer into a monomer by detergent induces release of the trapped preprotein. These results provide direct evidence that preproteins cross the bacterial membrane, associated with a translocation channel formed by a dimer of SecYEG.
Bessonneau
Pascal
P
Laboratoire Transports et Signalisations Cellulaires, IBBMC-CNRS UMR 8619, Université de Paris XI, Bâtiment 430, Orsay 91405, France.
Besson
Véronique
V
Collinson
Ian
I
Duong
Franck
F
D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000502:physiology; D001426:Bacterial Proteins; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000502:physiology; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry* / Q000502:physiology; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000502:physiology; D009038:Motion; D011487:Protein Conformation; D011498:Protein Precursors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D013329:Structure-Activity Relationship
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; C065493:SecE protein, E coli; C088616:SecG protein, E coli; C057841:SecY protein, E coli; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins