Iron-Sulfur Proteins: Investigations of Hyperfine-Shifted Hydrogen, Carbon, and Nitrogen Resonances

Abstract

Iron-sulfur proteins are present in almost all living organisms. They are characterized by one or more iron ions ligated to inorganic sulfur and/or cysteine sulfur. Rubredoxin-type clusters contain a single iron ligated to four cysteines and have no inorganic sulfur. All other types of iron-sulfur protein contain two or more irons plus inorganic sulfur. Four types of iron-sulfur centers with cysteine ligands to the protein have been characterized by x-ray crystallography; they can be distinguished by the number of iron and inorganic sulfur atoms as: [lFe], [2Fe-2S], [4Fe-4S], and [3Fe-4S. An additional type of iron-sulfur center has been shown to have one carboxylic acid ligand, and Rieske centers are believed to contain a [2Fe-2S] cluster ligated to two cysteines and two histidines. Some iron-sulfur proteins contain more than one Fe-S center, and these may be of the same or mixed types. Rubredoxins and all ferredoxins display electron- carrier activity but no classical enzyme function. Some iron-sulfur proteins, such as endonuclease III and aconitase, have been shown to play roles in enzymatic catalysis rather than in redox chemistry (Hentze & Argos, 1991). Other Fe-S proteins are involved in the regulation of transcription (Roualt et al., 1991).