Disease relevance of ECs4897

• Cellular import of colicin E3 is initiated by the Escherichia coli outer membrane cobalamin transporter, BtuB [1].
• The BtuB protein of Escherichia coli is a multifunctional outer membrane receptor required for the binding and uptake of vitamin B12, bacteriophage BF23, and the E colicins [2].
• BtuB is a TonB-dependent transport protein that binds and carries vitamin B(12) across the outer membrane of Gram negative bacteria such as Escherichia coli [3].
• Analyses of the primary sequence of hemoglobin-binding protein HgbA from Actinobacillus pleuropneumoniae by comparative modelling and by a Hidden Markov Model identified its topological similarities to bacterial outer membrane receptors BtuB, FepA, FhuA, and FecA of Escherichia coli [4].

High impact information on ECs4897

• We go on to delineate key features of the "colicin translocon" that assembles at the cell surface after BtuB binding by using a complex of histidine-tagged Im9 bound to ColE9S-S [5].
• The BtuB transporter mediates high-affinity binding and TonB-dependent active transport of vitamin B12 [cyanocobalamin (CNCbl)] across the outer membrane of Escherichia coli [6].
• An in vivo method of detecting substrate-induced changes in the Ton box environment measured reaction of a biotin maleimide derivative with cysteine substitutions through the N-terminal region of BtuB between positions 1 and 31 [6].
• Crosslinking at several positions was increased when BtuB was loaded with substrate, and the crosslinking pattern was altered by the presence of substitutions in BtuB that cause a TonB-uncoupled phenotype [7].
• Fluorescein-labeled E-peptide-1 binds to purified BtuB in a calcium-dependent manner with a Kd of 43.6 +/- 4.9 nm or 2370 +/- 670 nm in the presence or absence of calcium, respectively [8].

Chemical compound and disease context of ECs4897

• We had previously shown that the Escherichia coli proteins DcrA (SdaC) and DcrB, located, respectively, in the inner membrane and periplasm, are involved in the early development of virulent bacteriophage C1, which recognises BtuB as an outer membrane receptor [9].

Biological context of ECs4897

• An amino acid substitution within the conserved amino-terminal region of BtuB resulted in production of a receptor that had normal binding functions but was incapable of energy-dependent transport of vitamin B12 [10].
• We conclude that the BtuB binding sites for cobalamins and enzymatic E-colicins are overlapping but inequivalent and that the distal loop and (possibly) the short alpha-helical flanking regions are sufficient for high affinity binding [8].
• Mutations located in the minimum R domain that abolished or reduced the biological activity of colicin E9 similarly affected the competitive binding of the mutant colicin protein to BtuB [11].
• Homology searches of bacterial genomes, structural annotation based on the presence of conserved Cbl-binding residues identified by analysis of our BtuB structure, and detection of homologs of the periplasmic Cbl-binding binding protein BtuF enable identification of putative BtuB orthologs in enteric and non-enteric bacterial species [12].
• This suppression activity was associated with the plasmid, suggesting that a mutation within the tonB gene on the plasmid allowed the mutant BtuB receptor to function in the transport of the vitamin [13].

Anatomical context of ECs4897

• This binding event establishes a distinct RNA structure that is likely to be responsible for inhibition of ribosome binding and consequent reduction in synthesis of the cobalamin transport protein BtuB [14].
• This conformational change and the similarity in the EPR spectra between reconstituted and native membranes indicate that BtuB is correctly folded and functional in the reconstituted system [15].
• Transport of CN-Cbl across the outer membrane and its accumulation in the periplasm is mediated by the TonB-dependent transporter BtuB [16].
• Hybrid proteins in which various lengths from the amino terminus of BtuB were linked to alkaline phosphatase (btuB::phoA genes) were all secreted across the cytoplasmic membrane [17].

Associations of ECs4897 with chemical compounds

• Efficient purification of overexpressed BtuB containing stoichiometric levels of bound lipopolysaccharide has been achieved through the extraction of the outer membrane with nonionic detergent followed by ion-exchange chromatography [18].
• BtuB mutants were expressed, spin labeled, purified, and reconstituted into phosphatidylcholine [15].
• Here, we incorporate pairs of nitroxide spin labels into membrane reconstituted BtuB and utilize a four-pulse double electron-electron resonance (DEER) experiment to measure distances between the Ton box and the periplasmic surface of the transporter with and without substrate [3].
• Although CN-Cbl uptake does not inhibit ferrichrome uptake in wild-type cells, in which the amount of the outer membrane ferrichrome transporter FhuA far exceeds that of the cobalamin transporter BtuB, CN-Cbl does inhibit ferrichrome uptake when BtuB is overexpressed from a multicopy plasmid [19].
• BtuB was purified in the detergent LDAO (n-dodecyl-N,N-dimethylamine-N-oxide) and the complex was formed in a detergent mixture of LDAO and C8E4 (tetraethylene glycol monooctylether) [20].

Analytical, diagnostic and therapeutic context of ECs4897

• We report isothermal titration calorimetry data of BtuB binding the endonuclease toxin ColE9 and a disulfide form (ColE9S-S) where unfolding of the coiled-coil is prevented and, as a consequence, the toxin is biologically inactive [5].
• Crystallization and initial X-ray diffraction of BtuB, the integral membrane cobalamin transporter of Escherichia coli [21].
• The results of Western blotting detected a decrease in the protein expression levels of BtuB and OmpF involved in colicin translocation in the lon mutant [22].

References