Journal of Bacteriology, May 1999, p. 2895-2901, Vol. 181, No. 9
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Department of Microbiology and Immunology1 and Department of Medicine,3 University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, and Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 730192
Received 23 December 1998/Accepted 19 February 1999
FetA, formerly designated FrpB, an iron-regulated, 76-kDa
neisserial outer membrane protein, shows sequence homology to the TonB-dependent family of receptors that transport iron into
gram-negative bacteria. Although FetA is commonly expressed by most
neisserial strains and is a potential vaccine candidate for both
Neisseria gonorrhoeae and Neisseria
meningitidis, its function in cell physiology was previously
undefined. We now report that FetA functions as an enterobactin
receptor. N. gonorrhoeae FA1090 utilized ferric enterobactin as the sole iron source when supplied with ferric enterobactin at approximately 10 µM, but growth stimulation was abolished when an omega (
) cassette was inserted within
fetA or when tonB was insertionally
interrupted. FA1090 FetA specifically bound
59Fe-enterobactin, with a Kd of
approximately 5 µM. Monoclonal antibodies raised against the
Escherichia coli enterobactin receptor, FepA, recognized
FetA in Western blots, and amino acid sequence comparisons revealed
that residues previously implicated in ferric enterobactin binding by
FepA were partially conserved in FetA. An open reading frame downstream
of fetA, designated fetB, predicted a protein with sequence similarity to the family of periplasmic binding proteins
necessary for transporting siderophores through the
periplasmic space of gram-negative bacteria. An
insertion within
fetB abolished ferric enterobactin utilization without
causing a loss of ferric enterobactin binding. These data show that
FetA is a functional homolog of FepA that binds ferric enterobactin and
may be part of a system responsible for transporting the siderophore
into the cell.
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