Thermodynamic characterization of a tetrahaem cytochrome isolated from a facultative aerobic bacterium, Shewanella frigidimarina: a putative redox model for flavocytochrome c3

Pessanha, Miguel; Louro, Ricardo O.; Correia, Ilídio J.; Rothery, Emma L; Pankhurst, Kate; Reid, Gillian; Chapman, Stephen K; Turner, David L.; Salgueiro, Carlos A.

doi:10.1042/bj20021408

Cited by 23 publications

(34 citation statements)

References 59 publications

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“…The reduction of both proteins is faster at low pH, which is in agreement with the increase in the driving force known from the detailed thermodynamic characterization of both STCs, which showed that the reduction potentials are less negative at lower pH (10,11). However, the effect of protonation on the redox properties of the hemes at low pH is insufficient to fully account for the reduction rates, with this effect more pronounced for SfSTC.…”

Section: Resultssupporting

confidence: 85%

“…NMR data show that these conditions are met by both STCs studied in this work at the typical concentration used for stopped-flow experiments (10,11). For STC, the complete diagram of redox microstates involves 16 protonated and 16 deprotonated microstates (Fig.…”

Section: Methodsmentioning

confidence: 65%

“…With the full thermodynamic characterization in the physiological pH range, specific roles for the hemes were proposed, with heme I serving as the electron entry gate and heme IV as the electron exit (10). A similar situation was found for SfSTC, but the roles of the hemes I and IV are exchanged (11). Nevertheless, functional aspects of the redox activity of these proteins remain unexplored: do the intrinsic redox properties of the hemes lead to functional specificity as proposed on the basis of the thermodynamic characterization, or will this specificity arise only upon interaction with physiological partners?…”

mentioning

confidence: 78%

“…1). These are in fast equilibrium due to fast proton exchange, as deduced from NMR data (10,11). Upon reaction with the electron donor/acceptor these 32 microstates can be interconverted through 64 possible electron transfer microsteps.…”

Section: Methodsmentioning

confidence: 99%

“…In the oxidation process the driving force arises from the difference between the reduction potential of the heme and the reduction potential of the electron acceptor (e A ). The reduction potential of the heme that is being reduced/ oxidized in each particular microstep is given by the thermodynamic properties of the proteins, which are known from the literature and include the redox-Bohr effect (10,11). Therefore, each individual heme is characterized by a reference rate constant, k i 0 , on the assumption that the reorganization energy () and structural factors are essentially constant upon reduction or oxidation of the protein.…”

Section: Methodsmentioning

confidence: 99%

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Molecular Basis for Directional Electron Transfer

Paquete

Saraiva

Calçada

et al. 2010

Journal of Biological Chemistry

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Biological macromolecules involved in electron transfer reactions display chains of closely packed redox cofactors when long distances must be bridged. This is a consequence of the need to maintain a rate of transfer compatible with metabolic activity in the framework of the exponential decay of electron tunneling with distance. In this work intermolecular electron transfer was studied in kinetic experiments performed with the small tetraheme cytochrome from Shewanella oneidensis MR-1 and from Shewanella frigidimarina NCIMB400 using non-physiological redox partners. This choice allowed the effect of specific recognition and docking to be eliminated from the measured rates. The results were analyzed with a kinetic model that uses the extensive thermodynamic characterization of these proteins reported in the literature to discriminate the kinetic contribution of each heme to the overall rate of electron transfer. This analysis shows that, in this redox chain that spans 23 Å , the kinetic properties of the individual hemes establish a functional specificity for each redox center. This functional specificity combined with the thermodynamic properties of these soluble proteins ensures directional electron flow within the cytochrome even outside of the context of a functioning respiratory chain.Shewanella are facultative anaerobic ␥-proteobacteria capable of reducing a multitude of organic and inorganic substrates, including soluble and insoluble metallic compounds containing iron, manganese, uranium, or chromium (1). Shewanella arouse widespread interest in the science and in the engineering communities due to their role in geological phenomena such as global weathering and formation of minerals, their possible application in bioremediation of contaminated environments polluted with heavy metals, and their biotechnological applications for energy production in microbial fuel cells (1-3).The anaerobic respiratory flexibility found in these bacteria is associated with the presence of numerous multiheme cytochromes (4). One of the most abundant is the small tetraheme cytochrome (STC) 2 that has a 12-kDa molecular mass and contains four c-type hemes (5). Although the physiological role of STC in Shewanella oneidensis MR-1 (SoSTC) is still unknown, in S. frigidimarina NCIMB400 (SfSTC) it was shown to participate in iron respiration (6). The three-dimensional structure of SoSTC was determined for the reduced and oxidized states by x-ray crystallography (7), and recently the solution structure was solved for the reduced state of SfSTC (8). These studies showed that, despite the diversity found in the amino acid sequence of these cytochromes (64% identical), the architecture of their heme core is highly conserved with the hemes organized in a chain spanning 23 Å for the most distant heme irons (7,8). The determination of the structure of SoSTC led to the proposal that this protein may work as a nonspecific electron harvester (7). This proposal was refined by considering that hemes I-III would feed electrons to heme IV on t...

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Section: Resultssupporting

confidence: 85%

Section: Methodsmentioning

confidence: 65%

mentioning

confidence: 78%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Molecular Basis for Directional Electron Transfer

Paquete

Saraiva

Calçada

et al. 2010

Journal of Biological Chemistry

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Multi‐Heme Cytochromes & Enzymes

Pereira

Xavier

2005

Encyclopedia of Inorganic Chemistry

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Multiheme c cytochromes and enzymes are a diverse group of proteins having several hemes c covalently bound to the polypeptide chain that are either enzymes involved in redox chemistry or electron transfer proteins. Most known members of this group are associated with the respiratory chains of proteobacteria. These proteins are characterized by a low amino acid to heme ratio, bis‐histidinyl coordination (with a few exceptions), and low redox potentials of the hemes. The hemes are usually tightly packed in close contact, allowing very fast electron transfer. Despite the absence of overall sequence identity between proteins, the hemes are found in quite conserved structural motifs, which tend to be organized in diheme pairs that are either parallel or perpendicular to each other. From the structures available, two families can be recognized in terms of the heme structural arrangement: the cytochrome c 3 family where the perpendicular motif is predominant, and the hydroxylamine oxidoreductase (HAO) family where the stacked parallel motif alternates with the perpendicular motifs. Other multiheme cytochromes for which the structure is not yet available may be part of novel structural families.

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