The Pseudomonas aeruginosa tonB gene encodes a novel TonB protein.
The Pseudomonas aeruginosa tonB gene was cloned by complementation of the tonB mutation of Pseudomonas putida strain TE516 (W. Bitter, J. Tommassen & P.J. Weisbeek, 1993, Mol Microbiol 7, 117-130). The gene was 1025 bp in length, capable of encoding a protein of 36860 Da. As with previously described TonB proteins, the P. aeruginosa TonB (TonBp.a.) was rich in Pro residues (18.1%) and contained Glu-Pro/Lys-Pro repeats. Unlike previously described TonB proteins, however, TonBp.a. lacked an N-terminal membrane anchor (signal) sequence and contained, instead, a predicted internal signal/anchor sequence, expected to yield an atypical N-terminal cytoplasmic domain in this protein. TonB proteins are essential components in iron-siderophore uptake in bacteria, apparently functioning as energy transducers in coupling the energized state of the cytoplasmic membrane to outer-membrane receptor function. As expected, tonB derivatives of P. aeruginosa were defective in siderophore-mediated iron acquisition. tonB gene expression was inducible by iron-limitation, consistent with the identification of a Fur consensus binding sequence upstream of the gene. TonBp.a. showed substantially greater similarity to the Escherichia coli TonB protein than the Pseudomonas putida protein (31% identity vs. 20% identity) and tonBp.a. was able to complement deficiencies in the acquisition of ferric enterobactin and vitamin B12, and sensitivity to phage phi 80 of an E. coli tonB strain. The larger size of TonBp.a. and its ability to function in both E. coli and P. putida make it a unique TonB protein whose characterization should enhance our understanding of TonB function in bacteria.
Poole
Keith
K
Department of Microbiology and Immunology, Queen's University, Kingston, Ontario, K7L 3N6Canada.
Zhao
Qixun
Q
Department of Microbiology and Immunology, Queen's University, Kingston, Ontario, K7L 3N6Canada.
Neshat
Shádi
S
Department of Microbiology and Immunology, Queen's University, Kingston, Ontario, K7L 3N6Canada.
Heinrichs
David E
DE
Department of Microbiology and Immunology, Queen's University, Kingston, Ontario, K7L 3N6Canada.
Dean
Charles R
CR
Department of Microbiology and Immunology, Queen's University, Kingston, Ontario, K7L 3N6Canada.
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D007501:Iron / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D011550:Pseudomonas aeruginosa / Q000235:genetics*; D016958:Pseudomonas putida / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D017262:Siderophores / Q000378:metabolism; D013045:Species Specificity
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D017262:Siderophores; C057616:tonB protein, Bacteria; C489181:tonB protein, E coli; D007501:Iron