Classification of iron-sulfur cores in ferredoxins by 1H nuclear magnetic resonance spectroscopy.
A 1H nuclear magnetic resonance (NMR) study was carried out on various ferredoxins which possess one of three types of iron-sulfur clusters, (2Fe-2S), (3Fe-3S), or (4Fe-4S). In the isolated form, (2Fe-2S) ferredoxins from spinach (Spinacea oleracia), pokeweed (Phytolacca americana), a blue-green alga (Spirulina platensis), and a halobacterium (Halobacterium halobium) exhibited two broad resonances common in chemical shift at the region downfield of 10 ppm. In their reduced forms, seven contact-shifted resonances appeared spread over 30 ppm. Although the positions of the contact-shifted resonances in the reduced state differed among the four, a common trend in the temperature dependence of their resonance positions was recognized. Two (4Fe-4S) ferredoxins from Bacillus stearothermophilus and Bacillus thermoproteolyticus exhibited almost indistinguishable spectral patterns in both the oxidized and reduced forms. The ferricyanide-treated ferredoxins of B. stearothermophilus and B. thermoproteolyticus showed characteristic contact-shifted resonances distinct from the spectra of the original (4Fe-4S) ferredoxins. This corresponds to the recent finding of the interconversion of (4Fe-4S) and (3Fe-3S) clusters with ferricyanide in the ferredoxin. Based on our data together with reported NMR data on other ferredoxins, contact-shift resonances of three types of clusters were tabulated. The reliability of NMR classification increases when we compare the NMR spectra of a ferredoxin with the classification standards at the two redox states. Moreover, not only the absolute values of the chemical shifts of contact-shifted resonances but also their temperature dependence give distinctive information applicable to iron core identification.
D001395:Azotobacter / Q000378:metabolism; D001407:Bacillus / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism; D005288:Ferredoxins / Q000378:metabolism*; D001411:Geobacillus stearothermophilus / Q000378:metabolism; D006217:Halobacterium / Q000378:metabolism; D007501:Iron / Q000032:analysis*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D010944:Plants / Q000378:metabolism; D013455:Sulfur / Q000032:analysis*; D013696:Temperature
D005288:Ferredoxins; D013455:Sulfur; D007501:Iron