Contents -- Preface -- Contributing authors -- 1 Iron-sulfur proteins: a historical perspective -- 1.1 Framing the scene -- 1.2 The early days of "nonheme iron" -- 1.3 Of proteins and analogues -- 1.4 Beyond electron shuttles -- 1.5 How are FeS clusters synthesized in cells? -- Acknowledgment -- References -- 2 Chemistry of iron-sulfur clusters -- 2.1 Introduction -- 2.2 Electronic structure of Fe-S complexes -- 2.2.1 Spin-polarization and strong metal-ligand bonds -- 2.2.2 Spin-coupling and metal-metal bonds -- 2.2.3 Spin resonance delocalization in mixed-valence iron pairs -- 2.3 Unique properties of Fe-S clusters -- 2.3.1 Stable rigid clusters mean low reorganization energy -- 2.3.2 Polynuclear clusters mean multiple valency -- 2.3.3 Resonance delocalization and [Fe4S4(Cys)4] cluster conversion -- 2.4 Summary -- Acknowledgments -- References -- 3 Quantitative interpretation of EPR spectroscopy with applications for iron-sulfur proteins -- 3.1 Introduction -- 3.2 Basic EPR theory -- 3.3 g Factor anisotropy -- 3.4 Hyperfine structure -- 3.5 Ligand interactions -- 3.6 Spin Hamiltonian -- 3.7 Basic EPR instrumentation -- 3.8 Simulation of powder spectra -- 3.9 Quantitative aspects -- 3.10 Examples -- 3.10.1 S = 1/2 systems -- 3.10.2 Spin systems with S = 3/2, 5/2, 7/2, etc. -- 3.10.3 Spin systems with S = 1, 2, 3, etc -- 3.11 Conclusion -- References -- 4 The utility of Mössbauer spectroscopy in eukaryotic cell biology and animal physiology -- 4.1 Introduction -- 4.2 Transitions associated with MBS -- 4.3 Coordination chemistry of iron -- 4.4 Electron spin angular momentum and EPR spectroscopy -- 4.5 High-spin vs low-spin FeII and FeIII complexes -- 4.6 Isomer shift (d) and quadrupole splitting (ΔEQ) -- 4.7 Effects of a magnetic field -- 4.8 Slow vs fast relaxation limit.

4.9 MB properties of individual Fe centers found in biological systems -- 4.10 Magnetically interacting Fe aggregates -- 4.11 Insensitivity of MBS and a requirement for 57Fe enrichment -- 4.12 Invariance of spectral intensity among Fe centers -- 4.12.1 Mitochondria -- 4.12.2 Vacuoles -- 4.12.3 Whole yeast cells -- 4.12.4 Human mitochondria and cells -- 4.12.5 Blood -- 4.12.6 Heart -- 4.12.7 Liver -- 4.12.8 Spleen -- 4.12.9 Brain -- 4.13 Limitations of MBS and future directions -- Acknowledgments -- References -- 5 The interstitial carbide of the nitrogenase M-cluster: insertion pathway and possible function -- 5.1 Introduction -- 5.2 Proposed role of NifB in carbide insertion -- 5.3 Accumulation of a cluster intermediate on NifB -- 5.4 Investigation of the insertion of carbide into the M-cluster -- 5.5 Tracing the fate of carbide during substrate turnover -- References -- 6 The iron-molybdenum cofactor of nitrogenase -- 6.1 Introduction -- 6.2 The metal clusters of nitrogenase -- 6.3 Structure of FeMoco -- 6.4 Redox properties of FeMoco -- 6.5 An overlooked detail: the central light atom -- 6.6 The nature of X -- 6.7 Insights into the electronic structure of FeMoco -- 6.8 A central carbon - consequences and perspectives -- Acknowledgments -- References -- 7 Biotin synthase: a role for iron-sulfur clusters in the radical-mediated generation of carbon-sulfur bonds -- 7.1 Introduction -- 7.2 Sulfur atoms in biomolecules -- 7.3 Biotin chemistry and biosynthesis -- 7.4 The biotin synthase reaction -- 7.5 The structure of biotin synthase and the radical SAM superfamily -- 7.6 The [4Fe-4S]2+ cluster and the radical SAM superfamily -- 7.7 The [2Fe-2S]2+ cluster and the sulfur insertion reaction.

7.8 Characterization of an intermediate containing 9-MDTB and a [2Fe-2S]+ cluster -- 7.9 Other important aspects of the biotin synthase reaction -- 7.10 A role for iron-sulfur cluster assembly in the biotin synthase reaction -- 7.11 Possible mechanistic similarities with other sulfur insertion radical SAM enzymes -- Acknowledgment -- References -- 8 Molybdenum-containing iron-sulfur enzymes -- 8.1 Introduction -- 8.2 The xanthine oxidase family -- 8.2.1 D. gigas aldehyde:ferredoxin oxidoreductase -- 8.2.2 Bovine xanthine oxidoreductase -- 8.2.3 Aldehyde oxidases -- 8.2.4 CO dehydrogenase -- 8.2.5 4-Hydroxybenzoyl-CoA reductase -- 8.3 The DMSO reductase family -- 8.3.1 DMSO reductase and DMS dehydrogenase -- 8.3.2 Polysulfide reductase -- 8.3.3 Ethylbenzene dehydrogenase -- 8.3.4 Formate dehydrogenases -- 8.3.5 Bacterial nitrate reductases -- 8.3.6 Arsenite oxidase and arsenate reductase -- 8.3.7 Pyrogallol:phloroglucinol transhydroxylase -- 8.4 Prospectus -- References -- 9 The role of iron-sulfur clusters in the biosynthesis of the lipoyl cofactor -- 9.1 Introduction -- 9.2 Discovery of LA -- 9.3 Functions of the lipoyl cofactor -- 9.3.1 Primary metabolism -- 9.3.2 Antioxidant -- 9.4 Pathways for lipoyl cofactor biosynthesis -- 9.4.1 Exogenous pathway -- 9.4.2 Endogenous pathway -- 9.5 Characterization of LipA -- 9.5.1 Discovery of LipA -- 9.5.2 In vivo characterization of LipA -- 9.5.3 LipA is an iron-sulfur enzyme -- 9.5.4 LipA is an RS enzyme -- 9.5.5 Product inhibition of LipA -- 9.5.6 LipA contains two [4Fe-4S] clusters -- 9.5.7 Two distinct roles for the iron-sulfur clusters -- 9.5.8 A unique intermediate -- 9.5.9 A proposed mechanism for the biosynthesis of the lipoyl cofactor -- 9.6 Conclusions -- Acknowledgment -- References.

10 Iron-sulfur clusters and molecular oxygen: function, adaptation, degradation, and repair -- 10.1 Introduction -- 10.2 Fe-S clusters - reasons for their abundance -- 10.2.1 Origin of Fe-S clusters -- 10.2.2 Functions of Fe-S clusters -- 10.3 Oxygen and Fe-S clusters -- 10.3.1 Properties of molecular oxygen and its partially reduced species -- 10.3.2 Oxidative damage to Fe-S clusters -- 10.3.3 Molecular mechanisms of oxidative damage to Fe4S4 clusters -- 10.3.4 Fe3S4 to Fe2S2 cluster conversion in FNR -- 10.3.5 X-ray crystallographic studies -- 10.3.6 Alternative reactions can occur and compete -- 10.3.7 Structural changes -- 10.4 Adaptation to oxygen -- 10.4.1 Switch between metabolisms or restriction to niches -- 10.4.2 O2-tolerant NiFe hydrogenases -- 10.4.3 Protective systems against ROS -- 10.4.4 Evolutionary replacement of Fe-S clusters to keep essential functions in aerobic organisms -- 10.5 Conclusions -- References -- 11 A retrospective on the discovery of [Fe-S] cluster biosynthetic machineries in Azotobacter vinelandii -- 11.1 Introduction -- 11.2 An introduction to nitrogenase -- 11.3 Approaches to identify gene-product and product-function relationships -- 11.4 FeMoco and development of the scaffold hypothesis for complex [Fe-S] cluster formation -- 11.5 An approach for the analysis of nif gene product function -- 11.5.1 Phenotypes associated with loss of NifS or NifU function indicate their involvement in nitrogenase-associated [Fe-S] cluster formation -- 11.5.2 NifS is a cysteine desulfurase -- 11.5.3 Extension of the scaffold hypothesis to NifU function -- 11.5.4 Discovery of isc system for [Fe-S] cluster formation and functional cross-talk among [Fe-S] cluster biosynthetic systems -- 11.6 The Isc system is essential in A. vinelandii.

11.7 There is limited functional cross-talk between the Nif and Isc systems -- 11.8 Closing remarks -- Acknowledgments -- References -- 12 A stress-responsive Fe-S cluster biogenesis system in bacteria - the suf operon of Gammaproteobacteria -- 12.1 Introduction to Fe-S cluster biogenesis -- 12.2 Sulfur trafficking for Fe-S cluster biogenesis -- 12.3 Iron donation for Fe-S cluster biogenesis -- 12.4 Fe-S cluster assembly and trafficking -- 12.5 Iron and oxidative stress are intimately intertwined -- 12.6 Stress-response Fe-S cluster biogenesis in E. coli -- 12.7 Sulfur trafficking in the stress-response Suf pathway -- 12.8 Stress-responsive iron donation for the Suf pathway -- 12.8.1 SufD -- 12.8.2 Iron storage proteins -- 12.8.3 Other candidates -- 12.9 Unanswered questions about Suf and Isc roles in E. coli -- Acknowledgment -- References -- 13 Sensing the cellular Fe-S cluster demand: a structural, functional, and phylogenetic overview of Escherichia coli IscR -- 13.1 Introduction -- 13.2 General properties of IscR -- 13.3 [2Fe-2S]-IscR represses Isc expression via a negative feedback loop -- 13.4 IscR adjusts synthesis of the Isc pathway based on the cellular Fe-S demand -- 13.5 IscR has a global role in maintaining Fe-S homeostasis -- 13.6 Fe-S cluster ligation broadens DNA site specificity for IscR -- 13.7 Phylogenetic analysis of IscR -- 13.8 Binding to two classes of DNA sites allows IscR to differentially regulate transcription in response to O2 -- 13.9 Roles of IscR beyond Fe-S homeostasis -- 13.10 Additional aspects of IscR regulation -- 13.11 Summary -- Acknowledgments -- References -- 14 Fe-S assembly in Gram-positive bacteria -- 14.1 Introduction -- 14.2 Fe-S proteins in Gram-positive bacteria -- 14.3 Fe-S cluster assembly orthologous proteins -- 14.3.1 Clostridia-ISC system -- 14.3.2 Actinobacteria-SUF.

14.3.3 Bacilli-SUF.