NMR ASSIGNMENTS, SECONDARY STRUCTURE AND HYDRATION OF OXIDIZED ESCHERICHIA-COLI FLAVODOXIN

Recombinant flavodoxin from Escherichia coli was uniformly enriched wi th N-15 and C-13 isotopes and its oxidized form in aqueous solution in vestigated by three-dimensional NMR spectroscopy. Nearly complete H-1, N-15 and C-13 resonance assignments were obtained. The secondary stru cture was determined from chemical shift, NOE and (3)J(HNH alpha) coup ling constant data. Like homologous long-chain flavodoxins, E. coli fl avodoxin contains a five-stranded parallel beta-sheet and five helices . The beta-strands were found to comprise the residues 3-8, 29-34, 48- 56, 80-89, 114-116 and 141-145. The helices comprise residues 12-25, 4 0-45, 62-73, 98-108 and 152-166. The FMN-binding site was determined b y intermolecular NOEs and low-field shifted amide proton resonances in duced by the phosphoester group of the cofactor. The data are in good agreement with a previously predicted model of E. coli flavodoxin [Hav el, T. F. (1993) Mol. Sim. 10, 175-210]. The analysis of of water-flav odoxin NOEs revealed the presence of two, possibly three, buried hydra tion water molecules which are located at sites, where homologous flav odoxins from Anacystis nidulans and Anabena 7120 contain conserved hyd ration water molecules. One of these water molecules mediates hydrogen bonds between the protein backbone and the ribityl chain of the FMN c ofactor.