SecD and SecF are required for the proton electrochemical gradient stimulation of preprotein translocation.
AUTOR(ES)
Arkowitz, R A
RESUMO
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.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=394897Documentos Relacionados
- SecF stabilizes SecD and SecY, components of the protein translocation machinery of the Escherichia coli cytoplasmic membrane.
- SecD and SecF facilitate protein export in Escherichia coli.
- Export of the outer membrane lipoprotein is defective in secD, secE, and secF mutants of Escherichia coli.
- The secD locus of E. coli codes for two membrane proteins required for protein export.
- The secD locus of E.coli codes for two membrane proteins required for protein export.