OVERPRODUCTION OF THE PRISMANE PROTEIN FROM DESULFOVIBRIO-DESULFURICANS ATCC-27774 IN DESULFOVIBRIO-VULGARIS (HILDENBOROUGH) AND EPR SPECTROSCOPY OF THE [6FE-6S] CLUSTER IN DIFFERENT REDOX STATES

The Desulfovibrio desulfuricans ATCC 27774 prismane protein was isolat ed from a Desulfovibrio vulgaris (Hildenborough) strain that contained the gene for this protein in expression vector pSUP104. A redox titra tion demonstrated that the [Fe-S] cluster in this protein may attain f our different redox states, indicated as +3, +4, +5 and +6, with midpo int potentials for the transitions of approx. -220, +50/-25 and +370 m V, respectively. EPR spectra of the protein in the various redox state s are reminiscent of those of the D. vulgaris prismane protein (Pierik et al. (1992) fur. J. Biochem. 206, 705-719), but differ in details. In the +5-state, virtually all the iron is in a S = 9/2 spin state, in dicative for a cluster that is more complex than common [4Fe-4S] or [2 Fe-2S] clusters. Similarity of the EPR spectrum of the protein in the +3-state with those of inorganic [6Fe-6S] model compounds suggests tha t the cluster in the protein is also [6Fe-6S]. In the +4-state of the protein a broad signal due to an integer-spin system can be detected w ith normal-mode EPR. A dramatic sharpening-up and increase of intensit y of this band (g = 14.7) is observed with parallel-mode EPR. In accor dance with the chemically determined iron content of the protein (6.0 +/- 0.45 moles of iron/mole of protein), the spectroscopic data indica te one [6Fe-6S] cluster in this protein. We did not find evidence for a previous claim (Moura et al. (1992) J. Biol. Chem, 267, 4489-4496) t hat the D. desulfuricans protein contains two [6Fe-6S] clusters.