Identification of the btuCED polypeptides and evidence for their role in vitamin B12 transport in Escherichia coli

Abstract

Passage of vitamin B12 across the outer and cytoplasmic membranes of Escherichia coli occurs in two steps, each involving independent transport systems. Since the vitamin accumulated in btuC or btuD mutants is readily released from the cell by chase or osmotic shock and does not undergo the usual metabolic conversions, the products of these genes might participate in transport across the cytoplasmic membrane. Mutations Several genetic loci in Escherichia coli are required for the high-affinity and irreversible uptake of vitamin B12 (cyanocobalamin) across the outer and cytoplasmic membranes (4). The btuB gene encodes the 66,000-Mr outer membrane receptor protein for cobalamin and cobinamide, the E colicins, and bacteriophage BF23 (6,9,15,18). The tonB product is necessary for the energy-dependent transfer of cobalamin from the receptor into the periplasm (3, 25). This protein is also required for siderophore-mediated iron uptake (reviewed in reference 22). These iron uptake systems also employ specific receptors in the outer membrane as well as other gene products that mediate transport steps after receptor binding (10,24,29).The btuCD locus, located next to himA at min 37.4 on the E. coli chromosome map (2)

Genetic analysis, nucleotide sequence, and products of two Pseudomonas denitrificans cob genes encoding nicotinate-nucleotide: dimethylbenzimidazole phosphoribosyltransferase and cobalamin (5'-phosphate) synthase

“…The best match for CobV was between the first 100 residues and the carboxy-terminal sequence of BtuC (27.7% match) (20). BtuC was proposed to belong to a cytoplasmic membrane transport system involved in the uptake of vitamin B12 in E. coli (14). The homology might reveal a protein domain responsible for cobalamin affinity.…”

The pmrF polymyxin-resistance operon of Yersinia pseudotuberculosis is upregulated by the PhoP-PhoQ two-component system but not by PmrA-PmrB, and is not required for virulence

“…A contribution to polymyxin resistance was previously reported for the Salmonella pmrF gene cluster (Gunn et al, 1998). In the pathogenic yersiniae, the pmrF operon is inserted between the btuCDE operon (required for the passage of vitamin B 12 through the outer and inner bacterial membranes (de Veaux et al, 1986) and the nplC gene (encoding a putative lipoprotein of unknown function). An identical genetic organization was described very recently in the insect pathogen Photorhabdus luminescens (Derzelle et al, 2004).…”

Lipoic acid metabolism in Escherichia coli: isolation of null mutants defective in lipoic acid biosynthesis, molecular cloning and characterization of the E. coli lip locus, and identification of the lipoylated protein of the glycine cleavage system

“…In vitro transcription-translation reactions were carried out with S30 extracts obtained from Promega. Maxicell experiments were performed as described by DeVeaux et al (18). Radiolabeled proteins were analyzed on 16% polyacrylamide-sodium dodecyl sulfate (SDS) gels for polyacrylamide gel electrophoresis (PAGE).…”