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SecD and SecF are required for the proton electrochemical gradient stimulation of preprotein translocation.
Author(s) -
Arkowitz R.A.,
Wickner W.
Publication year - 1994
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 - 10.1002/j.1460-2075.1994.tb06340.x
Subject(s) - biology , electrochemical gradient , chromosomal translocation , transport protein , membrane protein , microbiology and biotechnology , biochemistry , membrane , gene
Mutations in secD and secF show impaired protein translocation across the inner membrane of Escherichia coli. We investigated the effect of SecD and SecF (SecD/F) depletion on preprotein translocation into inverted inner membrane vesicles (IMVs). Both IMVs and cells which were depleted of SecD/F were defective in their ability to maintain a proton electrochemical gradient. The translocation of pre‐maltose binding protein (preMBP), which is strongly delta microH+ dependent, showed a 5‐fold decreased rate with IMVs lacking SecD/F. In contrast, proteolytic processing of preMBP to MBP by leader peptidase was similar in IMVs containing and lacking SecD/F, consistent with earlier findings that only ATP‐dependent translocation is required for the initiation of translocation. In the absence of a delta microH+, with ATP as the sole energy source, preMBP translocation into IMVs which contained or were depleted of SecD/F was identical. Translocation of the precursor of outer membrane protein A (proOmpA) in the presence of subsaturating ATP also required a generated delta microH+ and, under these conditions, proOmpA translocation required SecD/F. With saturating concentrations of ATP, where delta microH+ has little effect on in vitro proOmpA translocation, SecD/F also had little effect on translocation. These results explain why SecD/F effects are precursor protein dependent in vitro.