Department of Chemistry, University of Georgia, Athens 30602.
The 25-kDa subunit of the proton-translocating NADH-quinone oxidoreductase (NDH-1) of Paracoccus denitrificans has been expressed in Escherichia coli and purified to homogeneity. EPR studies of the reduced recombinant protein indicated that the expressed subunit contains a single [2Fe-2S] cluster (Yano, T., Sled', V. D., Ohnishi, T., and Yagi, T. (1994) Biochemistry 33, 494-499). In this report, the electronic, magnetic, and vibrational properties of the [2Fe-2S]2+,+ center have been investigated by the combination of absorption, circular dichroism, variable-temperature magnetic circular dichroism, electron paramagnetic resonance, and resonance Raman spectroscopies and compared with a range of simple [2Fe-2S]-containing proteins. The results are consistent with coordination by two cysteinyl residues at both the reducible and nonreducible iron sites and reveal a striking similarity between the properties of the [2Fe-2S] cluster in the P. denitrificans NDH-1 25-kDa subunit and those of the subclass of ferredoxin-type [2Fe-2S] centers typified by Clostridium pasteurianum 2Fe ferredoxin. The four cyteines residues involved in cluster ligation in these proteins have been tentatively identified based on sequence homology considerations.