Analysis of the hyperfine-shifted nitrogen-15 resonances of the oxidized form of Anabaena 7120 heterocyst ferredoxin.
Hyperfine-shifted nitrogen signals have been detected in one-dimensional 15N NMR spectra of oxidized Anabaena 7120 heterocyst ferredoxin labeled uniformly with 15N. Several of these have been classified by amino acid type by reference to results from selective 15N-labeling studies. Remarkable agreement is seen between a dipole-dipole analysis of the 15N T1 relaxation and the distances of several of the nitrogens from the irons of the cluster as derived from the X-ray structure of this protein [Jacobson, B. L., Chae, Y. K., Markley, J. L., Rayment, I., & Holden, H. M. (1993) Biochemistry 32, 6788-6793]. The agreement is within experimental error for hyperfine-shifted nitrogens that are at least 4.2 A distant from either of the irons of the cluster; however, the simple model appears to fail for hyperfine-shifted nitrogens that are closer to the cluster. The failure of the model for short distances may stem either from a breakdown of the point-dipole approximation and/or from neglect of delocalization of unpaired electron density from the iron ions to other atoms. Even with the above limitations, dipolar analysis of 15N relaxation should provide useful distance constraints for solution-state studies of iron-sulfur proteins.
Chae
Y K
YK
Graduate Program in Biophysics, University of Wisconsin-Madison 53706.
Markley
J L
JL
D017033:Anabaena / Q000737:chemistry*; D001426:Bacterial Proteins; D005288:Ferredoxins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D009587:Nitrogen Isotopes; D010084:Oxidation-Reduction; D013816:Thermodynamics
D001426:Bacterial Proteins; D005288:Ferredoxins; D009587:Nitrogen Isotopes; C064537:petF protein, Anabaena