Import of biopolymers into Escherichia coli: nucleotide sequences of the exbB and exbD genes are homologous to those of the tolQ and tolR genes, respectively.
AUTOR(ES)
Eick-Helmerich, K
RESUMO
Escherichia coli with mutations in the exb region are impaired in outer membrane receptor-dependent uptake processes. They are resistant to the antibiotic albomycin and exhibit reduced sensitivity to group B colicins. A 2.2-kilobase-pair DNA fragment of the exb locus was sequenced. It contained two open reading frames, designated exbB and exbD, which encoded polypeptides of 244 and 141 amino acids, respectively. Both proteins were found in the cytoplasmic membrane. They showed strong homologies to the TolQ and TolR proteins, respectively, which are involved in uptake of group A colicins and infection by filamentous bacteriophages. exbB and exbD were required to complement exb mutations. Osmotic shock treatment rendered exb mutants sensitive to colicin M, which was taken as evidence that the ExbB and ExbD proteins are involved in transport processes across the outer membrane. It is concluded that the exb- and tol-dependent systems originate from a common uptake system for biopolymers.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=210325Documentos Relacionados
- Membrane topologies of the TolQ and TolR proteins of Escherichia coli: inactivation of TolQ by a missense mutation in the proposed first transmembrane segment.
- The structurally related exbB and tolQ genes are interchangeable in conferring tonB-dependent colicin, bacteriophage, and albomycin sensitivity.
- Point Mutations in Transmembrane Helices 2 and 3 of ExbB and TolQ Affect Their Activities in Escherichia coli K-12
- Energy-coupled transport across the outer membrane of Escherichia coli: ExbB binds ExbD and TonB in vitro, and leucine 132 in the periplasmic region and aspartate 25 in the transmembrane region are important for ExbD activity.
- Energy-Dependent Conformational Change in the TolA Protein of Escherichia coli Involves Its N-Terminal Domain, TolQ, and TolR