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Sec‐dependent membrane protein biogenesis: SecYEG, preprotein hydrophobicity and translocation kinetics control the stop‐transfer function
Author(s) -
Duong Franck,
Wickner William
Publication year - 1998
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/17.3.696
Subject(s) - translocase , biology , membrane transport protein , chromosomal translocation , translocase of the inner membrane , microbiology and biotechnology , transport protein , lipid bilayer , biophysics , biochemistry , membrane protein , translocase of the outer membrane , atp hydrolysis , translocon , protein targeting , membrane , mitochondrial membrane transport protein , atpase , gene , enzyme
Preprotein translocase catalyzes membrane protein integration as well as complete translocation. Membrane proteins must interrupt their translocation and be laterally released from the translocase into the lipid bilayer. We have analyzed the translocation arrest and lateral release activities of Escherichia coli preprotein translocase with an in vitro reaction and the preprotein proOmpA carrying a synthetic stop‐transfer sequence. Membrane protein integration is catalytic, occurs with kinetics similar to those of proOmpA itself and only requires the functions of SecYEG and SecA. Though a strongly hydrophobic segment will direct the protein to leave the translocase and enter the lipid bilayer, a protein with a segment of intermediate hydrophobicity partitions equally between the translocated and membrane‐integrated states. Analysis of the effects of PMF, varied ATP concentrations or synthetic translocation arrest show that the stop‐translocation efficiency of a mildly hydrophobic segment depends on the translocation kinetics. In contrast, the lateral partitioning from translocase to lipids depends solely on temperature and does not require SecA ATP hydrolysis or SecA membrane cycling. Thus translocation arrest is controlled by the SecYEG translocase activity while lateral release and membrane integration are directed by the hydrophobicity of the segment itself. Our results suggest that a greater hydrophobicity is required for efficient translocation arrest than for lateral release into the membrane.