MULTINUCLEAR MAGNETIC-RESONANCE STUDIES OF THE 2FE.2S-STAR FERREDOXIN FROM ANABAENA SPECIES STRAIN PCC-7120 .1. SEQUENCE-SPECIFIC H-1 RESONANCE ASSIGNMENTS AND SECONDARY STRUCTURE IN SOLUTION OF THE OXIDIZED FORM

Complete sequence-specific assignments were determined for the diamagnetic 1H resonances from Anabaena 7120 ferredoxin (Mr = 11 000). A novel assignment procedure was followed whose first step was the identification of the 13C spin systems of the amino acids by a 13C{13C} double quantum correlation experiment [Oh, B.-H., Westler, M. W., Darba, P., & Markley, J. L. (1988) Science 240, 908–911]. Then, the 1H spin systems of the amino acids were identified from the 13C spin systems by means of direct and relayed 1H{13C} single-bond correlations [Oh, B.-H., Westler, W. M., & Markley, J. L. (1989) J. Am. Chem. Soc. 111, 3083–3085]. The sequential resonance assignments were based mainly on conventional interresidue 1Hαi-1HNi+1 NOE connectivities. Resonances from 18 residues were not resolved in two-dimensional 1H NMR spectra. When these residues were mapped onto the X-ray crystal structure of the homologous ferredoxin from Spirulina platensis [Fukuyama, K., Hase, T., Matsumoto, S., Tsukihara, T., Katsube, Y., Tanaka, N., Kakudo, M., Wada, K., & Matsubara, H. (1980) Nature 286, 522–524], it was found that they correspond to amino acids close to the paramagnetic 2Fe•2S* cluster. Cross peaks in two-dimensional homonuclear 1H NMR spectra were not observed for any protons closer than about 7.8 Å to both iron atoms. Secondary structural features identified in solution include two antiparallel β-sheets, one parallel β-sheet, and one α-helix. © 1990, American Chemical Society. All rights reserved.