期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 275, 期 21, 页码 15669-15675出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.275.21.15669
关键词
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Class III anaerobic ribonucleotide reductase small component, named protein beta, contains a (4Fe-4S) center. its function is to mediate electron transfer from reduced flavodoxin to S-adenosylmethionine, required for the introduction of a glycyl radical in the large component, named protein or, which then becomes active for the reduction of ribonucleotides. By site-directed mutagenesis we demonstrate that the three cysteines of the conserved CXXXCXXC sequence are involved in iron chelation. Such a sequence is also present in the activase of the pyruvate formate-lyase and in the biotin synthase, both carrying an iron-sulfur center involved in reductive activation of S-adenosylmethionine. Even though they are able to bind iron in the (4Fe-4S) form, as shown by Mossbauer spectroscopy, the corresponding Cys to Ala mutants are catalytically inactive. Mutation of the two other cysteines of the protein did not result in inactivation. We thus conclude that the (4Fe-4S) cluster has, in the wild type protein, only three cysteine ligands and a fourth still unidentified ligand.
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