BACTERIAL IRON TRANSPORT - H-1-NMR DETERMINATION OF THE 3-DIMENSIONALSTRUCTURE OF THE GALLIUM COMPLEX OF PYOVERDIN G4R, THE PEPTIDIC SIDEROPHORE OF PSEUDOMONAS-PUTIDA G4R

Among the fluorescent Pseudomonas species, Pseudomonas putida is a rar e case of a nitrogen-fixing bacterium that transforms nitrogen into am monia. When grown under iron-deficient conditions, it produces two maj or pyoverdins: pyoverdin G4R and pyoverdin G4RA. Their primary structu res have been established using FAB-MS and one- and two-dimensional N- 15, C-13, and H-1 NMR on both the unlabeled and N-15-labeled compounds [Salah El Din, A. L,. M., et al. (1997) Tetrahedron 53, 12539-12552]. The two pyoverdins have a common chromophore derived from 2,3-diamino -6,7-dihydroxyquinoline. The chromophore is bound to the linear heptap eptide -D-beta-threo-OHAsp-L-Dab-Gly-L-Ser-L-cyclo-OHOrn. Circular dic hroism spectra suggest that the absolute configuration of the metal co mplex is Delta. The three-dimensional structure in solution of pyoverd in G4R-Ga(III) was determined after interpretation of two-dimensional H-1 NMR spectra recorded at 283 and 303 K. The complex is tightly defi ned with a compact structure with a Delta absolute configuration. The site of complexation of the metal ion is found to be located on the su rface of the molecule, showing that the ion can be released without la rge conformational changes, while the polar groups of the peptide chai n, which may be responsible for the recognition of the receptor, are p laced on the opposite side of the overall shape. The three-dimensional structure of pyoverdin G4R-Ga(III) is compared with those of other py overdins, and the role of the structure in iron uptake is discussed.