TAILIEUCHUNG - Báo cáo khoa học: Subunit composition and in vivo substrate-binding characteristics of Escherichia coli Tat protein complexes expressed at native levels

The Tat system transports folded proteins across the bacterial cytoplasmic membrane and the thylakoid membrane of plant chloroplasts. Substrates are targeted to the Tat pathway by signal peptides containing a pair of consecutive arginine residues. The membrane proteins TatA, TatB and TatC are the essential components of this pathway inEscherichia coli. | ễFEBS Journal Subunit composition and in vivo substrate-binding characteristics of Escherichia coli Tat protein complexes expressed at native levels Christopher A. McDevitt1 Grant Buchanan2 Frank Sargent3 Tracy Palmer2 3 and Ben C. Berks1 1 Department of Biochemistry University of Oxford UK 2 Department of Molecular Microbiology John Innes Centre Norwich UK 3 Schoolof BiologicalSciences University of East Anglia Norwich UK Keywords Escherichia coli protein targeting signal peptide Tat protein transport twin arginine translocation Correspondence B. C. Berks Department of Biochemistry University of Oxford South Parks Road Oxford OX1 3QU UK Fax 44 1865 275259 Tel 44 1865 275250 E-mail Present address Nuffield Department of ClinicalLaboratory Science John Radcliffe Hospital University of Oxford UK Received 9 August 2006 revised 18 October 2006 accepted 24 October 2006 doi The Tat system transports folded proteins across the bacterial cytoplasmic membrane and the thylakoid membrane of plant chloroplasts. Substrates are targeted to the Tat pathway by signal peptides containing a pair of consecutive arginine residues. The membrane proteins TatA TatB and TatC are the essential components of this pathway in Escherichia coli. The complexes that these proteins form at native levels of expression have been investigated by the use of affinity tag-coding sequences fused to chromosomal tat genes. Distinct TatA and TatBC complexes were identified using size-exclusion chromatography and shown to have apparent molecular masses of 700 and 500 kDa respectively. Following in vivo expression the Tat substrate protein SufI was found to copurify with the TatBC but not the TatA complex. This binding required the SufI signal peptide. Substitution of the twin-arginine residues in the SufI signal peptide by either twin lysine or twin alanine residues abolished export. However both variant SufI proteins still copurified with the TatBC .

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