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Evidence from Mössbauer spectroscopy for distinct [2Fe-2S](2+) and [4Fe-4S](2+) cluster binding sites in biotin
Natalia B Ugulava1, Kristene K Surerus, Joseph T Jarrett
1Johnson Research Foundation and Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Abstract:
Biotin synthase is an AdoMet-dependent radical enzyme that catalyzes the insertion of an FeS cluster-derived sulfur atom into dethiobiotin. The dimeric enzyme is purified containing one [2Fe-2S]2+ cluster per monomer, but it is most active when reconstituted with an additional [4Fe-4S]2+ cluster per monomer. Using Mössbauer spectroscopy coupled with differential reconstitution of each cluster with 57Fe, we show that the reconstituted enzyme has approximately 1:1 [2Fe-2S]2+ and [4Fe-4S]2+ clusters and that the [4Fe-4S]2+ cluster is assembled at an alternate site not previously occupied by the [2Fe-2S]2+ cluster. These data suggest that biotin synthase is evolved to simultaneously accommodate two different clusters with unique roles in catalysis.
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