Localization of functional domains in the XXXX @entity71221 receptor FhuE and the @entity15250 ferric-pseudobactin 358 receptor PupA.

@entity1522 @entity1472 @entity1473 @entity15250 @entity71221 @entity526
Transport of ferric-siderophores across the outer membrane of gram-negative bacteria is mediated by specific outer membrane receptors. To localize the substrate-binding domain of the ferric-pseudobactin 358 receptor, PupA, of @entity15250 WCS358, we constructed chimeric receptors in which different domains of PupA were replaced by the corresponding domains of the related ferric-pseudobactin receptors PupB and PupX, or the @entity71221 receptor FhuE of @entity526 . None of the chimeric proteins composed of pseudobactin receptor domains facilitated growth on any of the original substrates, or they showed only an extremely low efficiency. However, these receptors enabled cells of @entity15250 BN8 to grow on media supplemented with uncharacterized siderophore preparations. These siderophore preparations were isolated from the culture supernatant of WCS358 cells carrying plasmids that contain genes of @entity15250 B10 required for the biosynthesis of pseudobactin B10. Hybrid proteins that contained at least the @entity1472 -terminal 516 @entity1522 of mature FhuE were active as a receptor for @entity71221 and interacted with the @entity526 TonB protein. A chimeric PupA-FhuE protein, containing the @entity1472 -terminal 94 @entity1472 acids of mature PupA, was also active as a @entity71221 receptor, but only in the presence of @entity15250 TonB. It is concluded that the @entity1473 -terminal domain of ferric-pseudobactin receptors is important, but not sufficient, for ligand interaction, whereas binding of @entity71221 by the FhuE receptor is not dependent on this domain. Apparently, the ligand-binding sites of different receptors are located in different regions of the proteins. Furthermore, species-specific TonB binding by the PupA receptor is dependent on the @entity1472 -terminal domain of the receptor.
