Figure 5.
The enzyme PtaA is the periplasmic transaminase that converts the glutamic acid side chain of pyoverdine into the α-ketoglutaric acid variant. A, mass spectrometry results showing the UPLC chromatograms filtered for the masses of the succinamide, α-ketoglutaric acid, and glutamic acid variants on the left. On the right, the corresponding mass spectra of the peak at 0.6 min are depicted. The mass peaks were assigned to the structures shown in B and D. B, structure of the pyoverdine backbone, the intramolecular cyclized succinic acid variant, and the non-cyclized pyoverdine precursor ferribactin. The residues R1–4 correspond to the substructures shown in D. C, IEF gels visualized by pyoverdine fluorescence (left) and a CAS overlay assay (right). Numbers denote the identified pyoverdine variants, whose structures are represented in B in conjunction with D.