Iron-sulfur proteins model studies

Up to now, two types of iron compounds have been studied with ENDOR, namely heme compounds (hemoproteins and some heme model compounds) and iron-sulfur proteins. For comprehensive summaries of the corresponding EPR work, the reader is referred to the literature234-2371. 

This account will deal in turn with structural features of the one-iron, two-iron, four-iron and three-iron proteins, and also with the most important topic of interconversion between the three-iron and four-iron clusters. Model compounds will be described briefly. Finally, kinetic studies and the role of iron-sulfur proteins in complex enzymes will be discussed. 

Before leaving iron-sulfur proteins, we must mention the important contributions that model studies have made, in particular before protein X-ray structural data were available. For discrete clusters of the t5 pe formed by reaction 28.15 and shown in diagram 28.20, it is possible to investigate magnetic, electronic spectroscopic and electrochemical properties, record Fe Mossbauer spectra (see Section 2.12) and determine accurate structural data by X-ray diffraction. Working with metalloproteins is, of course, far more difficult. 

Iron-sulfur clusters appear in a great many proteins as both electron-transport and enzymatic sites see Iron-Sulfur Protein, for this reason there has been great interest for SOyears in the development and understanding of iron-sulfur model complexes. Both structure and properties of synthetic analogs of 1-, 2-, 3-, and 4-iron protein active sites have been studied extensively. This article will address the structural and chemical properties, synthesis, and catalytic activity of these synthetic analogs, as compared to the native protein-bound iron-sulfur cores. 

The ability to selectively enhance the modes of the resonant chromophore has fueled the steady development of RR spectroscopy and its transient RR and TR variants as exquisite probes of active site structure and dynamics in a wide range of metalloproteins and enzymes. Inasmuch as this remarkable potential has been more fully realized in the study of heme proteins than for any other class of metalloproteins, it is natural that the illustrative applications presented here be focused on these systems. However, excellent summaries of applications to other metalloproteins and their model compounds are available, including copper proteins,iron-sulfur proteins, and non-heme oxo-iron clusters. ... 

Y. Guo, Initial studies on iron sulfur proteins and related model compounds via 57Fe and 6INi synchrotron radiation based perturbed angular correlations (SRPAC), in nuclear resonant scattering on nitrogenase, hydrogenase and model systems, Ph.D. thesis, 2009. 

Electrochemical studies performed in the 7 x Cys-Aspl4 D. afri-canus Fdlll indicate that the reduced [3Fe-4S] center can react rapidly with Fe to form a [4Fe-4S] core that must include noncysteinyl coordination (101). The carboxylate side chain of Asp 14 was proposed as the most likely candidate, since this amino acid occupies the cysteine position in the typical sequence of a 8Fe protein as indicated before. The novel [4Fe-4S] cluster with mixed S and O coordination has a midpoint redox potential of 400 mV (88). This novel coordinated state with an oxygen coordination to the iron-sulfur core is a plausible model for a [4Fe-4S] core showing unusual spin states present in complex proteins (113, 114). 

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