CHARACTERIZATION AND REGULATION OF THE EXPRESSION OF FATB, AN IRON TRANSPORT PROTEIN ENCODED BY THE PJM1 VIRULENCE PLASMID

The pJM1-encoded genes fatDCBA are essential for iron acquisition via the siderophore anguibactin. Sequence analysis indicated that the open reading frame corresponding to the fatB gene possesses domains that a re characteristic of periplasmic proteins that bind the ferric siderop hore. In this work, a monospecific antiserum against an oligopeptide c ontaining the last 27 amino acids of the carboxy-terminal region from this open reading frame was used to demonstrate that fatB encodes a 35 kDa protein that is essential for iron transport. By using this antib ody we were able to demonstrate that expression of the fatB gene is ne gatively regulated by the Fur protein at high iron concentrations. Con versely, its expression was positively regulated by the combined actio n of the AngR protein and products of the TAF region. Fats, the produc t of the fatB gene, is isolated with the membrane fraction. In accorda nce with these findings is the fact that the first 23 amino acid resid ues of this protein have the properties of a lipoprotein signal sequen ce. The lipoprotein nature of FatB is supported by the fact that treat ment of Vibrio anguillarum cells with globomycin, an inhibitor of the lipoprotein signal peptidase, results in the accumulation of a 38 kDa pro-FatB precursor protein.