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Behaviour of topological marker proteins targeted to the Tat protein transport pathway
Author(s) -
Stanley Nicola R.,
Sargent Frank,
Buchanan Grant,
Shi Jiarong,
Stewart Valley,
Palmer Tracy,
Berks Ben C.
Publication year - 2002
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2002.02797.x
Subject(s) - periplasmic space , twin arginine translocation pathway , biology , protein subunit , membrane protein , biochemistry , transport protein , subcellular localization , membrane transport protein , signal peptide , vesicle associated membrane protein 8 , cytoplasm , microbiology and biotechnology , escherichia coli , peptide sequence , gene , membrane
Summary The Escherichia coli Tat system mediates Sec‐independent export of protein precursors bearing twin arginine signal peptides. Formate dehydrogenase‐N is a three‐subunit membrane‐bound enzyme, in which localization of the FdnG subunit to the membrane is Tat dependent. FdnG was found in the periplasmic fraction of a mutant lacking the membrane anchor subunit FdnI, confirming that FdnG is located at the periplasmic face of the cytoplasmic membrane. However, the phenotypes of gene fusions between fdnG and the subcellular reporter genes phoA (encoding alkaline phosphatase) or lacZ (encoding β ‐galactosidase) were the opposite of those expected for analogous fusions targeted to the Sec translocase. PhoA fusion experiments have previously been used to argue that the peripheral membrane DmsAB subunits of the Tat‐dependent enzyme dimethyl sulphoxide reductase are located at the cytoplasmic face of the inner membrane. Biochemical data are presented that instead show DmsAB to be at the periplasmic side of the membrane. The behaviour of reporter proteins targeted to the Tat system was analysed in more detail. These data suggest that the Tat and Sec pathways differ in their ability to transport heterologous passenger proteins. They also suggest that caution should be observed when using subcellular reporter fusions to determine the topological organization of Tat‐dependent membrane protein complexes.

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