Crystal structural Analysis of Ferredoxins Which Change the Structures of Active Center by Removing Iron Atom.

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Ferredoxins which change a (4Fe-4S) structure of clusters to another iron-sulfur cluster by removing an iron atom are divided into two groups. Peptococcus aerogenes and Bacillus thermoproteolyticus(B.t) ferredoxins, which have a sequence of ----Cys-X-X-Cys-X-X-Cys------Cys-Pro-- forming a (4Fe-4S) cluster, belong to the first group. Mycobacterium smegmatis ferredoxin as well as Azotobactor vinerandii ferredoxin, the sequence of which is replaced by Asp at a cysteinyl residue of the first group belongs to the second group.B.t ferredoxin was crystallized into the monoclinic system with the cell dimensions a=70.26, b=37.83, c=32.95 <゜!A> and <beta> =105.9゜ , and the space group C2. Intensity data for eight octants were collected up to 2.3 <゜!A> resolution. Correcting the observed structure factors for the absorption effect acording to North et al., they were averaged among equivalent reflections. The remaining systematic error in Bijvoet differences was reduced by the local scaling method. Phase angle of each reflection was determined by the native anomalous dispersion method coupled with phase information from partial structure. The molecular structure based on the 2.6 <゜!A> resolution map was refined by the restrained least-squares method by Konnert and Hendrickson at 2.3 <゜!A> resolution. Main chain folding of B. t ferredoxin is topologically similar to that of P. aerogenes (8Fe-8S) ferredoxin. One of two (4Fe-4S) cluster in (8Fe-8S) ferredoxin is replaced by an <alpha> -helix in B.t ferredoxin, which may has an important role to preserve the tertiary structure. Comparing several sequences of (4Fe-4S) ferredoxins, each ferredoxin seems to have a similar main chain folding to B.t ferredoxin.The crystals of M.s is the orthrombic system with cell dimensions, a=172.01, b=56.31 and c=102.38, and the space group C2221. Molecular packing in the crystal was determined by the native anomalous Patterson method.