The oligomeric distribution of SecYEG is altered by SecA and translocation ligands.
The multimeric membrane protein complex translocase mediates the transport of preproteins across and integration of membrane proteins into the inner membrane of Escherichia coli. The translocase consists of the peripheral membrane-associated ATPase SecA and the heterotrimeric channel-forming complex consisting of SecY, SecE and SecG. We have investigated the quaternary structure of the SecYEG complex in proteoliposomes. Fluorescence resonance energy transfer demonstrates that SecYEG forms oligomers when embedded in the membrane. Freeze-fracture techniques were used to examine the oligomeric composition under non-translocating and translocating conditions. Our data show that membrane-embedded SecYEG exists in a concentration-dependent equilibrium between monomers, dimers and tetramers, and that dynamic exchange of subunits between oligomers can occur. Remarkably, the formation of dimers and tetramers in the lipid environment is stimulated significantly by membrane insertion of SecA and by the interaction with translocation ligands SecA, preprotein and ATP, suggesting that the active translocation channel consists of multiple SecYEG complexes.
Scheuring
Johannes
J
Department of Chemistry, Technical University Munich, Lichtenbergstr. 4, 85747 Garching, Germany.
Braun
Nathalie
N
Nothdurft
Lars
L
Stumpf
Matthias
M
Veenendaal
Andreas K J
AK
Kol
Stefan
S
van der Does
Chris
C
Driessen
Arnold J M
AJ
Weinkauf
Sevil
S
D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer; D008024:Ligands; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D011510:Proteolipids / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008024:Ligands; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011510:Proteolipids; D000069816:SEC Translocation Channels; C065493:SecE protein, E coli; C088616:SecG protein, E coli; C057841:SecY protein, E coli; C020485:proteoliposomes; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins