TAILIEUCHUNG - Báo cáo Y học: Defective translocation of a signal sequence mutant in a prlA4 suppressor strain of Escherichia coli

In the accompanying paper [Adams, H., Scotti, ., de Cock, H., Luirink, J. & Tommassen, J. (2002)Eur. J. , 5564–5571.], we showed that the precursor of outer-membrane proteinPhoEofEscherichia coliwithaGly to Leu substitution at position )10 in the signal sequence (G-10L) is targeted to the SecYEGtranslocon via the signal-recognition particle (SRP) route, instead of via the SecB pathway. Here, we studied the fate of the mutant precursor in aprlA4mutant strain. | Eur. J. Biochem. 269 5572-5580 2002 FEBS 2002 doi Defective translocation of a signal sequence mutant in a prlA4 suppressor strain of Escherichia coli Hendrik Adams1 Pier A. Scotti2 Joen Luirink2 and Jan Tommassen1 1 Department of Molecular Microbiology and Institute of Biomembranes Utrecht University The Netherlands department of Microbiology Institute of Molecular Biological Sciences Biocentrum Amsterdam The Netherlands In the accompanying paper Adams H. Scotti . de Cock H. Luirink J. Tommassen J. 2002 Eur. J. Bio-chem. 269 5564-5571. we showed that the precursor of outer-membrane protein PhoE of Escherichia coli with a Gly to Leu substitution at position -10 in the signal sequence G-10L is targeted to the SecYEG translocon via the signalrecognition particle SRP route instead of via the SecB pathway. Here we studied the fate of the mutant precursor in aprlA4 mutant strain. prlA mutations located in the secY gene have been isolated as suppressors that restore the export of precursors with defective signal sequences. Remarkably the G-10L mutant precursor which is normally exported in a wild-type strain accumulated strongly in a prlA4 mutant strain. In vitro cross-linking experiments revealed that the precursor is correctly targeted to the prlA4 mutant translocon. However translocation across the cytoplasmic membrane was defective as appeared from proteinase K-accessibility experiments in pulse-labeled cells. Furthermore the mutant precursor was found to accumulate when expressed in a secY40 mutant which is defective in the insertion of integral-membrane proteins but not in protein translocation. Together these data suggest that SecB and SRP substrates are differently processed at the SecYEG translocon. Keywords inner membrane prlA4 protein insertion protein translocation Sec translocon. Most proteins destined for the periplasm or the outer membrane of Escherichia coli are transported across the inner membrane by the .

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