This Article Full Text (PDF) Other Versions of this Article: JB.00180-07v1 189/13/4662    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Vakharia-Rao, H. Articles by Postle, K. Search for Related Content PubMed PubMed Citation Articles by Vakharia-Rao, H. Articles by Postle, K.

 Previous Article  |  Next Article 

J. Bacteriol. doi:10.1128/JB.00180-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Deletion and Substitution Analysis of the Escherichia coli TonB-Q160 Region

School of Molecular Biosciences, Washington State University, Pullman, WA 99164; Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802

^* To whom correspondence should be addressed. Email: postle{at}psu.edu.

	Abstract

Active transport of iron siderophores and vitamin B12 across the outer membrane (OM) of Escherichia coli requires OM transporters and the potential energy of the cytoplasmic membrane (CM) proton gradient and CM proteins TonB, ExbB, and ExbD. A region at the amino terminus of the transporter, called the TonB box, directly interacts with TonB-Q160 region residues. R158 and R166 in the TonB-Q160 region were proposed to play important roles in structures of the TonB carboxy terminus with OM transporters BtuB and FhuA. In contrast to predictions based on crystal structures, none of the single, double or triple alanyl substitutions at arginyl residues significantly decreased TonB activity. Even the quadruple mutant TonB-R154A, R158A, R166A, R171A still retained 30% activity. Up to 5 residues centered on TonB-Q160 could be deleted without inactivating TonB or preventing its association with the outer membrane. TonB mutants with nested deletions of 7, 9 or ll residues centered on TonB-Q160 were inactive and appeared to never have associated with the OM. Because the 7-residue deletion (TonB7, residues S157-Y163) can still form disulfide-linked dimers when combined with W213C or F202C in the TonB carboxy terminus, the TonB7 deletion did not prevent necessary energy-dependent conformational changes that occur in the CM. Thus it appeared that initial contact with the OM was made through TonB residues S157-Y163. It is hypothesized that the TonB-Q160 region could therefore be part of a large disordered region required to span the periplasm and contact an OM transporter.

This article has been cited by other articles:

• Brinkman, K. K., Larsen, R. A. (2008). Interactions of the Energy Transducer TonB with Noncognate Energy-Harvesting Complexes. J. Bacteriol. 190: 421-427 [Abstract] [Full Text]