Two-dimensional magnetization exchange spectroscopy of Anabaena 7120 ferredoxin. Nuclear Overhauser effect and electron self-exchange cross peaks from amino acid residues surrounding the 2Fe-2S* cluster.
Hyperfine 1H NMR signals of the 2Fe-2S* vegetative ferredoxin from Anabaena 7120 have been studied by two-dimensional (2D) magnetization exchange spectroscopy. The rapid longitudinal relaxation rates of these signals required the use of very short nuclear Overhauser effect (NOE) mixing times (0.5-20 ms). The resulting pattern of NOE cross-relaxation peaks when combined with previous 1D NOE results [Dugad, L. B., La Mar, G. N., Banci, L., & Bertini, I. (1990) Biochemistry 29, 2263-2271] led to elucidation of the carbon-bound proton spin systems from each of the four cysteines ligated to the 2Fe-2S* cluster in the reduced ferredoxin. Additional NOE cross peaks were observed that provide information about other amino acid residues that interact with the iron-sulfur cluster. NOE cross peaks were assigned tentatively to Leu27, Arg42, and Ala43 on the basis of the X-ray coordinates of oxidized Anabaena 7120 ferredoxin [Rypniewski, W.R., Breiter, D.R., Benning, M.M., Wesenberg, G., Oh, B.-H., Markley, J.L., Rayment, I., & Holden, H. M. (1991) Biochemistry 30, 4126-4131]. Three chemical exchange cross peaks were detected in magnetization exchange spectra of half-reduced ferredoxin and assigned to the 1H alpha protons of Cys49 and Cys79 [both of whose sulfur atoms are ligated to Fe(III)] and Arg42 (whose amide nitrogen is hydrogen-bonded to one of the inorganic sulfurs of the 2Fe-2S* cluster). The chemical exchange cross peaks provide a means of extending assignments in the spectrum of reduced ferredoxin to assignments in the spectrum of the oxidized protein.(ABSTRACT TRUNCATED AT 250 WORDS)
Skjeldal
L
L
National Magnetic Resonance Facility at Madison, Institute for Enzyme Research, Biochemistry Department, University of Wisconsin, Madison 53706.
Westler
W M
WM
Oh
B H
BH
Krezel
A M
AM
Holden
H M
HM
Jacobson
B L
BL
Rayment
I
I
Markley
J L
JL
D000409:Alanine / Q000737:chemistry; D001120:Arginine / Q000737:chemistry; D001665:Binding Sites; D000458:Cyanobacteria; D003545:Cysteine / Q000737:chemistry; D005288:Ferredoxins / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D007930:Leucine / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010084:Oxidation-Reduction; D013057:Spectrum Analysis; D013455:Sulfur / Q000737:chemistry
D005288:Ferredoxins; D013455:Sulfur; D001120:Arginine; D007501:Iron; D007930:Leucine; D003545:Cysteine; D000409:Alanine