scholarly journals Pore-forming activity of the Tsx protein from the outer membrane of Escherichia coli. Demonstration of a nucleoside-specific binding site.

1988 ◽  
Vol 263 (5) ◽  
pp. 2493-2499
Author(s):  
C Maier ◽  
E Bremer ◽  
A Schmid ◽  
R Benz
Keyword(s):  
Escherichia Coli ◽  
Binding Site ◽  
Outer Membrane ◽  
Specific Binding

scholarly journals Evaluation of the rate constants of sugar transport through maltoporin (LamB) of Escherichia coli from the sugar-induced current noise.

1995 ◽  
Vol 105 (3) ◽  
pp. 385-401 ◽  
Author(s):  
C Andersen ◽  
M Jordy ◽  
R Benz
Keyword(s):  
Escherichia Coli ◽  
Binding Site ◽  
Outer Membrane ◽  
Rate Constants ◽  
Sugar Transport ◽  
Current Noise ◽  
Induced Current ◽  
Lipid Bilayer Membranes ◽  
Sugar Binding ◽  
Different Temperatures

LamB (maltoporin) of Escherichia coli outer membrane was reconstituted into artificial lipid bilayer membranes. The channel contains a binding site for sugars and is blocked for ions when the site is occupied by a sugar. The on and off reactions of sugar binding cause an increase of the noise of the current through the channel. The sugar-induced current noise of maltoporin was used for the evaluation of the sugar-binding kinetics for different sugars of the maltooligosaccharide series and for sucrose. The on rate constant for sugar binding was between 10(6) and 10(7) M-1.s-1 for the maltooligosaccharides and corresponds to the movement of the sugars from the aqueous phase to the central binding site. The off rate (corresponding to the release of the sugars from the channel) decreased with increasing number of glucose residues in the maltooligosaccharides from approximately 2,000 s-1 for maltotriose to 180 s-1 for maltoheptaose. The kinetics for sucrose movement was considerably slower. The activation energies of the stability constant and of the rate constants for sugar binding were evaluated from noise experiments at different temperatures. The role of LamB in the transport of maltooligosaccharides across the outer membrane is discussed.

scholarly journals Defined Inactive FecA Derivatives Mutated in Functional Domains of the Outer Membrane Transport and Signaling Protein of Escherichia coli K-12

2004 ◽  
Vol 186 (16) ◽  
pp. 5303-5310 ◽  
Author(s):  
Annette Sauter ◽  
Volkmar Braun
Keyword(s):  
Escherichia Coli ◽  
Binding Site ◽  
Outer Membrane ◽  
Crystal Structures ◽  
Transcription Initiation ◽  
Ferric Citrate ◽  
Globular Domain ◽  
Salt Bridges ◽  
The Individual ◽  
K 12

ABSTRACT The FecA outer membrane protein of Escherichia coli functions as a transporter of ferric citrate and as a signal receiver and signal transmitter for transcription initiation of the fec transport genes. Three FecA regions for which functional roles have been predicted from the crystal structures were mutagenized: (i) loops 7 and 8, which move upon binding of ferric citrate and close the entrance to the ferric citrate binding site; (ii) the dinuclear ferric citrate binding site; and (iii) the interface between the globular domain and the β-barrel. Deletion of loops 7 and 8 abolished FecA transport and induction activities. Deletion of loops 3 and 11 also inactivated FecA, whereas deletion of loops 9 and 10 largely retained FecA activities. The replacement of arginine residue R365 or R380 and glutamine Q570, which are predicted to serve as binding sites for the negatively charged dinuclear ferric citrate, with alanine resulted in inactive FecA, whereas the binding site mutant R438A retained approximately 50% of the FecA induction and transport activities. Residues R150, E541, and E587, conserved among energy-coupled outer membrane transporters, are predicted to form salt bridges between the globular domain and the β-barrel and to contribute to the fixation of the globular domain inside the β-barrel. Mutations E541A and E541R affected FecA induction and transport activity slightly, whereas mutations E587A and E587R more strongly reduced FecA activity. The double mutations R150A E541R and R150A E587R nearly abolished FecA activity. Apparently, the salt bridges are less important than the individual functions these residues seem to have for FecA activity. Comparison of the properties of the FecA, FhuA, FepA, and BtuB transporters indicates that although they have very similar crystal structures, the details of their functional mechanisms differ.

scholarly journals Bacterial SPOR domains are recruited to septal peptidoglycan by binding to glycan strands that lack stem peptides

2015 ◽  
Vol 112 (36) ◽  
pp. 11347-11352 ◽  
Author(s):  
Atsushi Yahashiri ◽  
Matthew A. Jorgenson ◽  
David S. Weiss
Keyword(s):  
Escherichia Coli ◽  
Bacillus Subtilis ◽  
Cell Division ◽  
Binding Site ◽  
Bacterial Cell ◽  
Specific Binding ◽  
Bacterial Cell Division ◽  
Target Proteins ◽  
Division Site ◽  
Lytic Transglycosylase

Bacterial SPOR domains bind peptidoglycan (PG) and are thought to target proteins to the cell division site by binding to “denuded” glycan strands that lack stem peptides, but uncertainties remain, in part because septal-specific binding has yet to be studied in a purified system. Here we show that fusions of GFP to SPOR domains from theEscherichia colicell-division proteins DamX, DedD, FtsN, and RlpA all localize to septal regions of purified PG sacculi obtained fromE.coliandBacillus subtilis. Treatment of sacculi with an amidase that removes stem peptides enhanced SPOR domain binding, whereas treatment with a lytic transglycosylase that removes denuded glycans reduced SPOR domain binding. These findings demonstrate unequivocally that SPOR domains localize by binding to septal PG, that the physiologically relevant binding site is indeed a denuded glycan, and that denuded glycans are enriched in septal PG rather than distributed uniformly around the sacculus. Accumulation of denuded glycans in the septal PG of bothE.coliandB.subtilis, organisms separated by 1 billion years of evolution, suggests that sequential removal of stem peptides followed by degradation of the glycan backbone is an ancient feature of PG turnover during bacterial cell division. Linking SPOR domain localization to the abundance of a structure (denuded glycans) present only transiently during biogenesis of septal PG provides a mechanism for coordinating the function of SPOR domain proteins with the progress of cell division.

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