The bacterial protein-translocation complex: SecYEG dimers associate with one or two SecA molecules.
In bacteria, the Sec-protein transport complex facilitates the passage of most secretory and membrane proteins across and into the plasma membrane. The core complex SecYEG forms the protein channel and engages either ribosomes or the ATPase SecA, which drive translocation of unfolded polypeptide chains through the complex and into the periplasmic space. Escherichia coli SecYEG forms dimers in membranes, but in detergent solution the population of these dimers is low. However, we find that stable dimers can be assembled by the addition of a monoclonal antibody. Normally, a stable SecYEG-SecA complex can only form on isolated membranes or on reconstituted proteo-liposomes. The antibody-stabilised SecYEG dimer binds one SecA molecule in detergent solution. In the presence of AMPPNP, a non-hydrolysable analogue of ATP, a complex forms containing one antibody and two each of SecYEG and SecA. SecYEG monomers or tetramers do not associate to a significant degree with SecA. The observed variability in the stoichiometry of SecYEG and SecA association and its nucleotide modulation may be important and necessary for the protein translocation reaction.
Tziatzios
Christos
C
Institute für Biophysik, JWG-Universität, 60590 Frankfurt am Main, Germany.
Schubert
Dieter
D
Lotz
Mirko
M
Gundogan
Derya
D
Betz
Heidi
H
Schägger
Hermann
H
Haase
Winfried
W
Duong
Franck
F
Collinson
Ian
I
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000906:Antibodies / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D002850:Chromatography, Gel; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D026901:Membrane Transport Proteins / Q000378:metabolism*; D021381:Protein Transport; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D012996:Solutions; D014461:Ultracentrifugation
D000906:Antibodies; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; D012996:Solutions; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins