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Review
. 2014 Apr 23;114(8):4366-469.
doi: 10.1021/cr400479b.

Metalloproteins containing cytochrome, iron-sulfur, or copper redox centers

Jing Liu  1 , Saumen Chakraborty, Parisa Hosseinzadeh, Yang Yu, Shiliang Tian, Igor Petrik, Ambika Bhagi, Yi Lu
Affiliations
Review

Metalloproteins containing cytochrome, iron-sulfur, or copper redox centers

Jing Liu et al. Chem Rev. .
No abstract available

PubMed Disclaimer

Figures

Figure 1
Figure 1
Reduction potential range of redox centers in electron transfer processes.
Figure 2
Figure 2
Representative pyridine hemochromogen spectra of hemin cofactors: (A) heme b, (B) heme a, and (C) heme d1. The spectrum of pyridine ferrohemochrome c is similar to that of heme b. Reprinted with permission from ref (116). Copyright 1992 Springer-Verlag.
Figure 3
Figure 3
Different types of heme found in cytochromes.
Figure 4
Figure 4
Commonly found heme axial ligands in various cytochromes. (A) Class I cyts c (PDB ID 3CYT) uses His/Met axial ligation. (B) Cyts b and multiheme cyts c contain bis-His ligation (bovine liver cyt b5, PDB ID 1CYO). (C) An unusual His/amine ligation is found only in cyt f (PDB ID 1HCZ). (D) Bis-Met ligation is encountered in bacterioferritin (PDB ID 1BCF). For c-type cytochromes the conserved -Cys-Xxx-Xxx-Cys-His- ligation and its covalent linkage to the heme via Cys residues are shown.
Figure 5
Figure 5
Schematic representations of various classes of cyts c. (A) Class I cyt c fold with His/Met heme axial ligands (PDB ID 3CYT). Mitochondrial designation of the helices is also shown. (B) Four-helix bundle cyt c′ belongs to class II cyt c having a 5c heme with His120 as the sole axial ligand (PDB ID 1E83). (C) Tetraheme cyt c3 belongs to class III cyt c with bis-His ligation to all four hemes (PDB ID 1UP9). Hemes I and III are attached to the protein via the highly conserved -Cys-Xxx-Xxx-Cys-His- sequence, whereas hemes II and IV are covalently bound to the protein by a -Cys-Xxx-Xxx-Xxx-Xxx-Cys-His- motif. In (A)–(C) the covalent attachment of the heme to the protein via Cys residues is shown. (D) Tetraheme cyt c from the photosynthetic reaction center (RC) belongs to class IV cyt c. Hemes I, II, and III have His/Met axial ligands, while heme IV has bis-His axial ligation to the heme iron (PDB ID 2JBL). (E) Cyt c554 from Nitrosomonas europaea belongs to a class of its own. Hemes I, III, and IV have bis-His-ligated heme iron, whereas heme II is 5c with His as the only axial ligand (PDB ID 1BVB). Heme numbering in (C)–(E) is according to their attachment occurring along the protein’s primary sequence. (F) Cyt f from chloroplast is unique from all other classes of cytochromes in that it mostly contains β-sheets and the heme is 6c with a His and N-terminal backbone NH2 group of a Tyr residue (PDB ID 1HCZ). It has been included as a subclass of cyt c because the heme is covalently bound to the protein via the highly conserved -Cys-Xxx-Xxx-Cys-His- signature motif for heme attachment ubiquitously found in c-type cytochromes.
Figure 6
Figure 6
Overall structural overlay of the reduced (cyan, PDB ID 1YCC) and oxidized (orange, PDB ID 2YCC) iso-1-cyt c (left). A close look at the heme site and the nearby residues is shown on the right along with some hydrogen bond interactions.
Figure 7
Figure 7
X-ray structure of cyt c-dependent NOR (cNOR) (PDB ID 3O0R) from Ps. aeruginosa.
Scheme 1
Scheme 1. Scheme Showing the Oxidation of Sulfite to Sulfate by Cyt c in Sulfite Oxidase
Reprinted from ref (273). Copyright 1996 American Chemical Society.
Figure 8
Figure 8
(A) X-ray structure of triheme cyt c7 (PDB ID 1HH5). All the hemes are bis-His-ligated. Cyt c7 is a minimized version of cyt c3 where heme II is missing. (B) Spatial arrangement of the four hemes in flavocytochrome c3 fumarate reductase (PDB ID IQO8). The heme irons of the heme pair II and III are in close proximity at 9 Å from each other, and the heme edges are 4 Å away.
Figure 9
Figure 9
(A) Schematic model for DMSO reduction by DmsEFAB and iron reduction by MtrABC(DEF). Flows of electrons are shown with arrows. DmsE and MtrA(D) are proposed to accept electrons from the menaquinone pool via CymA. Multiheme groups in CymA, MtrACDF, and DmsE are shown. IM = inner membrane, and OM = outer membrane. (B) “Staggered-cross” orientation of the hemes in outer membrane decaheme MtrF (PDB ID 3PMQ). Heme numbering is shown as Roman numerals, heme–iron distances are shown in orange, and distances between heme edges are shown in blue. (A) Reprinted with permission from ref (315). Copyright 2012 Biochemical Society. (B) Adapted from ref (316) Copyright 2011 National Academy of Sciences.
Figure 10
Figure 10
Schematic representation of the X-ray structure of bovine cyt b5 that belongs to the α + β class (PDB ID 1CYO). Two hydrophobic core domains, six α-helices, five β-strands, and 6c bis-His-ligated heme are shown. Adapted from ref (357). Copyright 2011 American Chemical Society.
Figure 11
Figure 11
Two orientation isomers (A and B forms) of heme observed in solution studies of the soluble fragment of cyt b5. The two isomers are related by a 180° rotation around the α,γ-meso-carbon atoms.
Figure 12
Figure 12
NMR structure of the antiparallel four-helix bundle cyt b562 (PDB ID 1QPU). His/Met axial coordination to the heme iron is shown.
Figure 13
Figure 13
Structural models of designed cytochrome models in de novo scaffolds. (A) A design model for a homodimeric four-helix tetraheme binding protein inspired by cyt bc1. Remade from coordinates courtesy of G. Ghirlanda and W. F. DeGrado. (B) Schematic representation of monomeric four-α-helix maquettes used to mimic ET cytochromes. Reprinted with permission from ref (406). Copyright 2013 Macmillan Publishers Ltd. (C) Crystal structure of Co(II) mimichrome IV (PDB 1PYZ).
Figure 14
Figure 14
Structural models of designed cytochrome models in native scaffolds. (A) X-ray crystallographic model of a pig myoglobin designed to have cytochrome-like bis-His ligation (PDB ID 1MNI). (B) Molecular dynamics model of a histidine mutant of the membrane protein, glycophorin A, designed to bind heme in a cytochrome-like manner. Coordinates provided by courtesy of G. Ghirlanda.
Figure 15
Figure 15
Crystal structure of CpRd (PDB ID 1IRO) at 1.1 Å resolution. (a) Overall fold of chain A of CpRd. The Fe(Cys)4 center is displayed as a ball-and-stick representation. (b) NH···S H-bond interactions around the Fe(Cys)4 center of CpRd. The side chains of C6, C39, V8, Y11, L41, and V44 are omitted for clarity. Color code: Fe, green; C, cyan; S, yellow, O, red; N, blue.
Figure 16
Figure 16
Representative spectra of rubredoxins. (a) UV–vis spectra of ferric and ascorbate reduced ferrous (inset) CpRd. (b) Mössbauer spectra of dithionite reduced ferrous CpRd measured at 4.2 K under a magnetic field applied parallel to the γ-rays. Reprinted from ref (623). Copyright 2002 American Chemical Society. (c) EPR spectra of CpRd. Reprinted with permission from ref (611). Copyright 1996 Elsevier.
Figure 17
Figure 17
Crystal structure of desulforedoxin from Dv. gigas (PDB ID 1DXG). The [FeCys4] centers are displayed in ball-and-stick mode and denoted. The backbones of coordinating cysteines are omitted for clarity. Color code for the ball-and-stick mode: cyan, carbon; green, iron; yellow, sulfur.
Figure 18
Figure 18
Structures of three classes of [2Fe–2S] ferredoxins. Notice that, in their physiological form, thioredoxin-like ferredoxins function as a dimer.
Figure 19
Figure 19
Structure of ferredoxin (right) cross-linked to FNR (left), PDB ID 3W5U. As shown, red acidic patches of ferredoxin are positioned in contact with blue basic residues of FNR. A zoomed-in figure of the region containing the cofactors (Fe–S and FAD) is shown at the bottom.
Figure 20
Figure 20
Structure of PSI (PDB ID 1JB0). The top left figure shows the overall structure, and the bottom figure shows all the cofactors in the system. The top right figure shows the PsaC, PsaD, and PsaE sites with FA and FB. Ferredoxin binds in the interface between PsaC, PsaD, and PsaE.
Figure 21
Figure 21
Structure of adrenodoxin (right) in complex with adrenodoxin reductase (left) (PDB ID 1E6E). As shown, red acidic patches of adrenodoxin are positioned against blue basic residues of adrenodoxin reductase. A zoom-in region of the cofactors (Fe–S and FAD) is shown at the bottom.
Figure 22
Figure 22
H-bonding network in plant-type ferredoxins.
Figure 23
Figure 23
Representative spectra of [2Fe–2S] ferredoxins: (a) UV–vis spectra of reduced (thin line) and oxidized (thick line) forms of ferredoxin from Aquifex aeolicus; (b) X-band EPR of [2Fe–2S]+ ferredoxin from Aq. aeolicus at 20 K; (c) Mössbauer of the [2Fe–2S]2+ state of ferredoxin from Aq. aeolicus at 4.2 K in zero field (upper) and an 8.0 T applied field parallel to the observed γ radiation (lower). Reprinted from ref (728). Copyright 2002 American Chemical Society.
Figure 24
Figure 24
Structures of the five classes of two-subunit ferredoxins.
Figure 25
Figure 25
Consensus sequences in ferredoxins. Reprinted with permission from ref (740). Copyright 2007 University Science Books.
Figure 26
Figure 26
Representative spectra of [4Fe–4S] proteins. (a, left) UV–vis of the oxidized form. Reprinted with permission from ref (760) Copyright 2005 Springer-Verlag. (b, middle) EPR of the [4Fe–4S]1+ state. Reprinted with permission from ref (761). Copyright 1999 Elsevier. (c, right) Mössbauer of the [4Fe−4S]2+ cluster of the E. coli FNR protein, T = 4.2 K (top), and the [4Fe−4S]1+ cluster of E. coli sulfite reductase, T = 110 K (bottom). Reprinted with permission from ref (529). Copyright 1997 American Association for the Advancement of Science.
Figure 27
Figure 27
Representative spectra of the [3Fe–4S] cluster. (a, left top) UV–vis of the oxidized form and (b, right) temperature-dependent EPR of the [3Fe–4S]1+ cluster. Reprinted with permission from ref (762). Copyright 2002 Elsevier. (c, left bottom) Mössbauer of the [3Fe–4S]1+ (top) and [3Fe–4S]0 (bottom) clusters . Reprinted with permission from ref (529). Copyright 1997 American Association for the Advancement of Science.
Figure 28
Figure 28
Minimal Rieske fold with three β-sheets and loops coordinating the [2Fe–2S] cluster with two His ligands and two Cys ligands (from PDB ID 1NDO).
Figure 29
Figure 29
Structure of the bc1 complex from chicken (PDB ID 3H1J) and its Rieske protein and Rieske center (left) and structure of the b6f complex from Mastigocladus laminosus (PDB ID 1VF5) and its Rieske protein and Rieske center (right).
Figure 30
Figure 30
Structure of naphthalene 1,2-dioxygenase (PDB ID 1NDO), the archetype of Rieske-type proteins from two different views, and a close-up of the active site Rieske center.
Figure 31
Figure 31
Interface between two monomers of naphthalene dioxygenase, NDO. Asp205 from the polypeptide chain on the left bridges two His residues that are ligands to the Fe–S cluster and catalytic nonheme iron center (PDB ID 1NDO).
Figure 32
Figure 32
Differences in the H-bond pattern between the Rieske fragment of naphthalene dioxygenase, NDO (PDB ID 2NDO), the water-soluble Rieske fragment of the bc1 complex, ISF (PDB ID 1RIE), and the Rieske fragment from the b6f complex, RFS (PDB ID 1RFS). Reprinted with permission from ref (773). Copyright 1999 Elsevier.
Figure 33
Figure 33
Representative spectra of Rieske centers. (a) UV–vis of the reduced (lower spectrum) and oxidized (upper spectrum) forms. Reprinted with permission from ref (866). Copyright 2004 National Academy of Sciences. (b) EPR of the reduced form. Reprinted with permission from ref (867). Copyright 2007 National Academy of Sciences. (c) Mössbauer of the [2Fe−2S]+ cluster of the Rieske protein from Ps. mendocina at T = 200 K. Reprinted with permission from ref (529). Copyright 1997 American Association for the Advancement of Science.
Figure 34
Figure 34
Structure of reduced (PDB ID 1HRR) and oxidized (PDB ID 1NER) HiPIP from Ch. vinosum (top left and top right, respectively). The overlay of the structures and zoom-in of the Fe–S cluster are shown at the bottom. As shown, only slight structural changes occurred upon reduction.
Figure 35
Figure 35
Proposed ET pathway in Dv. gigas [NiFe] hydrogenase. Selected distances are given in angstroms. PDB ID 1FRV. Color code: Fe, green; Ni, gray blue; C, cyan; S, yellow, O, red; N, blue. Reprinted with permission from ref (940). Copyright 1995 Macmillan Publishers Ltd.
Figure 36
Figure 36
(a) Crystal structure of O2-tolerant membrane-bound hydrogenase from Ralstonia eutropha (PDB ID 3RGW). Reprinted from ref (945). Copyright 2013 American Chemical Society. (b) Reduced [4Fe–3S] cluster from MBH (PDB ID 3AYX) (Reprinted with permission from ref (946). Copyright 2012 Wiley-VCH) and (c) oxidized [4Fe–3S] cluster from MBH (PDB ID 3AYZ). Reprinted with permission from ref (946). Copyright 2012 Wiley-VCH. Color code: Fe, green; C, cyan; S, yellow; N, blue; Ni, orange.
Figure 37
Figure 37
(a) Location of Fe–S clusters in [FeFe] hydrogenase (PDB ID 1FEH). (b) Proposed ET pathways for [FeFe] hydrogenase. Reprinted with permission from ref (958). Copyright 1998 American Association for the Advancement of Science.
Figure 38
Figure 38
(a) Overall structure of nitrogenase (PDB ID 1N2C). Cofactors are shown as spheres and denoted. Reprinted with permission from ref (965). Copyright 1997 Macmillan Publishers Ltd. (b) Reduced P cluster from nitrogenase (PDB ID 3U7Q) (Reprinted with permission from ref (946). Copyright 2012 Wiley-VCH.) and (c) oxidized P cluster from nitrogenase (PDB ID 2MIN). Reprinted with permission from ref (946). Copyright 2012 Wiley-VCH.
Figure 39
Figure 39
(a) Crystal structure of Rs. rubrum Ni CODH. Clusters are shown as spheres. PDB ID 1JQK. (b) [4Fe–5S–Ni] cluster C of Ca. hydrogenoformans Ni CODH. PDB ID 1SU8. (c) [4Fe–4S–Ni] cluster C of M. thermoacetica Ni CODH. PDB ID 1MJG. Reprinted with permission from ref (990). Copyright 2011 Elsevier.
Figure 40
Figure 40
Hybrid clusters in HCP. (a) Overall structure of as-isolated Dv. vulgaris HCP. Metal clusters are shown as spheres. PDB ID 1W9M. (b) Superposition of Dv. vulgaris HCP (cyan) and NiCODH (red, PDB code 1SU7). (c) Hybrid cluster in the as-isolated oxidized form of Dv. vulgaris HCP prepared anaerobically. PDB ID 1W9M. (d) Hybrid cluster in the reduced form of Dv. vulgaris HCP. PDB ID 1OA1. Residue backbones are omitted for clarity. Bonds inside the cluster are shown as dotted lines, and bonds between residues and the cluster are shown as solid lines. Color code: Fe, green; C, cyan; S, yellow; O, red; N, blue. Reprinted with permission from ref (995). Copyright 2008 International Union of Crystallography.
Figure 41
Figure 41
(a) Structure of siroheme. (b) Siroheme and the [4Fe–4S] cluster of spinach nitrite reductase. PDB ID 2AKJ. Color code: Fe, green; C, cyan; S, yellow; O, red; N, blue.
Figure 42
Figure 42
(a) Siroheme group and [4Fe–4S] cluster of DsrI. PDB ID 3OR1. (b) Sirohydrochlorin group and [4Fe–4S] cluster of DsrII. PDB ID 3OR2. (c) Siroheme group and [3Fe–4S] cluster of DsrII. PDB ID 3OR2. Color code: Fe, green; C, cyan; S, yellow; O, red; N, blue.
Figure 43
Figure 43
Crystal structure of mitochondrial respiratory complex I from T. thermophilus. PDB ID 4HEA. Cofactors involved in the ET pathway are shown on the right side with distances and directions denoted. Reprinted with permission from ref (1022). Copyright 2013 Elsevier.
Figure 44
Figure 44
Crystal structure of mitochondrial respiratory complex II. FAD binding protein (Fp) is shown in blue, iron–sulfur protein (Ip) is shown in cream, hydrophobic domains are shown in pink and orange, and the putative membrane is shown in gray shading. PDB ID 1ZOY. Cofactors involved in the ET pathway are shown on the right side, with distances, reduction potential, and directions denoted. Reprinted with permission from ref (1024). Copyright 2005 Elsevier.
Figure 45
Figure 45
Domain arrangement of type 1 copper protein. Reprinted with permission from ref (1119). Copyright 2006 Wiley-VCH.
Figure 46
Figure 46
Crystal structures of the T1 copper proteins. The secondary structure (α-helix and β-sheet) is shown in cartoon format, copper is shown as a purple ball, and ligands are shown in stick format. The name of the protein and its PDB ID are given below each structure.
Figure 47
Figure 47
Topology diagram showing the scheme of the secondary structure of azurin. β-Strands are shown as arrows, and the α-helix is shown as a cylinder. Copper ligands between β-strands 3 and 4 and between β-strands 7 and 8 are shown as blue polygons, while copper is shown as a purple circle.
Figure 48
Figure 48
T1 copper centers in plastocyanin, azurin, plantacyanin, and amicyanin. Reprinted with permission from ref (1119). Copyright 2006 Wiley-VCH.
Figure 49
Figure 49
H-bonding around Cys112 (A) and other ligands (B) of azurin. PDB ID 4AZU.
Figure 50
Figure 50
Electronic absorption (A) and EPR (B) spectra of azurin.
Figure 51
Figure 51
Structures of plastocyanin (left) and the complex of plastocyanin and cyt f (right). Left: copper ion is represented as a purple ball, His87 and Tyr 83 are represented in licorice format, and residues in two acidic patches are represented as ball and stick models. Right: plastocyanin is colored cyan, and cyt f is orange. The copper ion and His87 from plastocyanin and heme from cyt f are also shown.
Figure 52
Figure 52
Domain organization and copper center distribution in multicopper oxidases. Reprinted with permission from ref (1265). Copyright 2011 Wiley-VCH.
Figure 53
Figure 53
Active site of the multicopper oxidases. Cu sites are shown as green spheres. Figure generated from the crystal structure of ascorbate oxidase (PDB ID 1AOZ). Reprinted from ref (1264). Copyright 2007 American Chemical Society.
Figure 54
Figure 54
Crystal structures of (A) the oxidized red copper site in nitrosocyanin, (B) the oxidized T1 copper site in plastocyanin, and (C) the reduced red copper site in nitrosocyanin. Reprinted from ref (1271). Copyright 2005 American Chemical Society.
Figure 55
Figure 55
Active sites of type 2, type 1, and the newly constructed type 0 copper. In the center, a plot shows (in the shaded ovals) the typical values of two electron paramagnetic resonance spectroscopy parameters, A∥ and g∥, for type 1 (lower) and type 2 (upper) copper sites and the values of type 0 copper (green, red, and black points, right center), showing that type 0 copper does not fall into the typical ranges for these other kinds of sites. Reprinted with permission from ref (1308). Copyright 2009 Macmillan Publishers Ltd.
Figure 56
Figure 56
X-ray structures of Az and selected variants. (a) Native azurin (PDB ID 4AZU). (b) N47S/M121L azurin (PDB ID 3JT2). (c) N47S/F114N azurin (PDB ID 3JTB). (d) F114P/M121Q azurin (PDB ID 3IN0). Copper is shown in green, carbon in cyan, nitrogen in blue, oxygen in red, and sulfur in yellow. Hydrogen-bonding interactions are shown by dashed red lines. Reprinted with permission from ref (1088). Copyright 2009 Macmillan Publishers Ltd.
Figure 57
Figure 57
Reduction potentials for a number of Az mutants versus a measure of the hydrophobicity (log P), revealing the linear trend with respect to the axial position (residue 121). Reprinted with permission from ref (1088). Copyright 2009 Macmillan Publishers Ltd.
Figure 58
Figure 58
Illustration of the experimentally derived covalent and nonlocal electrostatic contributions to E° for the variants of Az relative to WT Az and their comparison to calculations. Reprinted from ref (1316). Copyright 2012 American Chemical Society.
Figure 59
Figure 59
Ligand and loop structure in different T1 copper proteins, CuA from T. thermophilus heme–copper oxidase, and red copper protein nitrosocyanin: (A) amicyanin (PDB ID 1AAC); (B) pseudoazurin (PDB ID 1PAZ); (C) plastocyanin (PDB ID 1PLC); (D) azurin (PDB ID 2AZA); (E) rusticyanin (PDB ID 1RCY); (F) CuA from T. thermophilus heme–copper oxidase (PDB ID 1CUA); (G) nitrosocyanin (PDB ID 1IBY).
Figure 60
Figure 60
Crystal structures of cytochrome c oxidase (PDB ID 3HB3) and nitrous oxide reductase (PDB ID 1FWX). The CuA sites are highlighted (copper is in green, sulfur is in yellow, nitrogen is in blue, and carbon is in cyan).
Figure 61
Figure 61
(A) Crystal structure of the biosynthetic model of the CuA site in azurin (PDB ID 1CC3). (B) Comparison of UV–vis spectra between the soluble CuA domain in cytochrome c oxidase (green line), wild-type azurin (blue line), and the biosynthetic CuA model in azurin (purple line). (C) Comparison of X-band CW EPR between wild-type azurin (blue line) and the biosynthetic CuA model in azurin (purple line), four-line splitting vs seven-line splitting. Reprinted with permission from ref (1365). Copyright 2010 Springer-Verlag.
Figure 62
Figure 62
Tuning the reduction potential at blue copper azurin and CuA azurin by redesigning the second coordination sphere. The effects of these mutants are in the same direction, but the magnitude is smaller in the CuA site due to the electron delocalization between the two copper ions. Adapted with permission from ref (1385). Copyright 2012 The Royal Society of Chemistry.
Figure 63
Figure 63
Schematic model of different states of the CuA center in cytochrome c oxidase: (A) mixed-valence form at neutral pH and (B) trapped-valence form at low pH. Subunit I is in light blue, and subunit II is in pink. Black arrows represent the flow of electrons, and orange arrows represent the flow of protons. Reprinted with permission from ref (1390). Copyright 2004 National Academy of Sciences.
Figure 64
Figure 64
Proposed mechanism of copper incorporation into the biosynthetic CuA model in azurin. Reprinted with permission from ref (103). Copyright 2012 Elsevier.
Figure 65
Figure 65
Cyt c oxidase from Pa. denitrificans (PDB ID 3HB3). The ET pathway is shown with arrows.
Figure 66
Figure 66
Bovine cytochrome bc1 complex (PDB ID 1BE3). Different ET domains and their cofactors are shown. bL = low-potential heme, bH = high-potential heme, and Q = ubiquinol. Electron transfer pathways are shown with arrows.
Figure 67
Figure 67
Schematic cycle of Rieske positions in the bc1 complex. Reprinted from ref (865). Copyright 2013 American Chemical Society.
Figure 68
Figure 68
Cyt b6f complex in the photosynthetic electron transport chain. P680 = reaction center chlorophylls of PSII, QA, QB = quinones of PSII, PQ/PQH2 pool = plastoquinone/plastoquinol pool, Fe–S = Rieske cluster, f = cyt f of the high-potential chains (blue arrows), Qp, Qn = plastoquinol oxidation and plastoquinone reduction sites, bp, bn, cn = hemes of the low-potential chain (red arrows), Fd = ferredoxin, and P700 = reaction center chlorophylls of PSI. The domain movement of the Rieske protein is shown by a two-sided arrow. The direction of proton translocation across the membrane is shown by proton arrows. The electronegative (cytoplasmic) (n) and electropositive (luminal) (p) sides of the membrane are labeled, and ET pathways are shown by arrows. A possible direct ET path from PSI to the cyt b6f complex is shown as the dashed line from Fd to the Qn site. Reprinted with permission from ref (1477). Copyright 2012 Springer Science+Business Media.
Figure 69
Figure 69
Environment around the heme of cyt f (PDB ID 1HCZ). Hydrophobic residues are shown as gray sticks. The “edge-to-face” interaction at 4 Å between Phe4 and the heme that is proposed to be important to tune the reduction potential of the heme iron is shown. The five conserved molecules that have been proposed to act as “proton wires” that couple ET with proton transfer are shown as red spheres. Residue numbering of waters is arbitrary.
Figure 70
Figure 70
Overall structure of Fdh-N from E. coli. Cofactors are displayed as spheres and denoted accordingly on the right. The putative membrane is shown in gray shading. PDB ID 1KQF. Reprinted with permission from ref (1492). Copyright 2002 American Association for the Advancement of Science.
Figure 71
Figure 71
Overall three-dimensional structure of NarGHI from E. coli K12. PDB ID 1Q16. Subunit and cofactor names are denoted. Reprinted with permission from ref (1505). Copyright 2006 Elsevier.
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