Mechanism and Biological Role of Nitric Oxide Binding to Cytochrome <i>c‘</i>

“…The wild type RC strain was further shown to produce N 2 O when grown in the presence of NO, leading to the suggestion that RCCP is involved in reductase activity (8). Particularly since NO-reductase activity has not been demonstrated for purified RCCP or any other cytochrome cЈ, it is possible that cytochrome cЈ could be a transporter coupled to a NO reductase, as recently proposed for the species Chromatium vinosum (53) and Rhodobacter sphaeroides (54). In the context of a physiological NO binding role for AXCP, the overall picture is that the distal side controls the initial NO binding, whereas the proximal heme pocket controls the release of NO with the ability of trapping and gating NO despite its close proximity to solvent with a virtually unidirectional release of NO.…”

mentioning

confidence: 93%

Molecular Basis for Nitric Oxide Dynamics and Affinity with Alcaligenes xylosoxidans Cytochrome c´

Kruglik

Lambry

Cianetti

et al. 2007

Journal of Biological Chemistry

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The bacterial heme protein cytochrome c from Alcaligenes xylosoxidans (AXCP) reacts with nitric oxide (NO) to form a 5-coordinate ferrous nitrosyl heme complex. The crystal structure of ferrous nitrosyl AXCP has previously revealed that NO is bound in an unprecedented manner on the proximal side of the heme. To understand how the protein structure of AXCP controls NO dynamics, we performed absorption and Raman timeresolved studies at the heme level as well as a molecular computational dynamics study at the entire protein structure level. We found that after NO dissociation from the heme iron, the structure of the proximal heme pocket of AXCP confines NO close to the iron so that an ultrafast (7 ps) and complete (99 ؎ 1%) geminate rebinding occurs, whereas the proximal histidine does not rebind to the heme iron on the timescale of NO geminate rebinding. The distal side controls the initial NO binding, whereas the proximal heme pocket controls its release. These dynamic properties allow the trapping of NO within the protein core and represent an extreme behavior observed among heme proteins.Nitric oxide (NO) acts as a second messenger in several physiological systems (1, 2), is involved in the production of several cytotoxic chemical species and nitrosative stress (3), and appears as an intermediate in the denitrification process (4). Cells have, thus, developed numerous heme proteins whose diverse functions involve nitric oxide binding and/or release. In some bacteria heme sensors were recently discovered (5) with a femtomolar affinity for NO, whereas cytochromes cЈ able to bind NO are found in many nitrogen-fixing, denitrifying, and photosynthetic bacteria (6). Although the physiological role the bacterial cytochrome cЈ from Alcaligenes xylosoxidans (AXCP) 2 is not yet established, the homologous cytochrome cЈ from Rhodobacter capsulatus has been shown to increase the resistance of this bacteria against NO toxicity (7,8). Thus, the bacterial cytochromes cЈ are inferred to disclose a particular behavior regarding NO dynamics and affinity. How heme proteins interact with NO and control its reactivity is ultimately related to their structure and the heme surroundings. A wide range of affinity and kinetic constants can be observed that correlates with the molecular dynamics of NO within the protein core. A striking example of this diversity is offered when comparing the NO dynamics governed by the enzyme NO synthase (9), the endogenous cellular source, and the NO receptorsoluble guanylate cyclase (10) (sGC) whose heme cofactor has a somewhat opposite role. Nitrosylated heme proteins usually form 6-coordinate complexes having histidine and NO as axial ligands at the proximal and distal sides of the heme, respectively (6c-NO-His), but some become 5-coordinate (5c) with NO (5c-NO) like sGC (11, 12) and AXCP (13,14). These latter proteins have an overall structure that presumably controls the strain upon the proximal histidine. Although sGC and AXCP possess different sequences and tertiary structures, they share the pro...

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“…Despite their ubiquity in bacteria, the biological role of cytochromes c¢ remains unclear. Although a role in electron transfer processes had been assumed for a long time [7], more recently it has been suggested that cytochromes c¢ are involved in protection against high levels of NO [8,9]. Scientific interest in cytochromes c¢ has increased further owing to the similarities in spectral properties and ligand binding properties between cytochrome c¢ from Alcaligenes xylosoxidans and sGC [10,11].…”

Section: Introductionmentioning

confidence: 99%

“…Most cytochromes c¢ are isolated as stable homodimers, although some occur as monomers or as a mixture of both [16]. Cytochrome c¢ from the purple photosynthetic bacterium Allochromatium vinosum (cyt-c¢) displays a unique dimer-to-monomer transition upon binding of NO, CO, CN -or small alkyl isocyanides [9,[17][18][19]. Like in many gas-sensing proteins [4,20], the selectivity in ligand binding arises from steric hindrance of the vacant coordination site [21].…”

Section: Introductionmentioning

confidence: 99%

Ligand-induced monomerization of Allochromatium vinosum cytochrome c′ studied using native mass spectrometry and fluorescence resonance energy transfer

et al. 2007

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Cytochrome c¢ from Allochromatium vinosum is an attractive model protein to study ligand-induced conformational changes. This homodimeric protein dissociates into monomers upon binding of NO, CO or CN -to the iron of its covalently attached heme group. While ligand binding to the heme has been well characterized using a variety of spectroscopic techniques, direct monitoring of the subsequent monomerization has not been reported previously. Here we have explored two biophysical techniques to simultaneously monitor ligand binding and monomerization. Native mass spectrometry allowed the detection of the dimeric and monomeric forms of cytochrome c¢ and even showed the presence of a CO-bound monomer. The kinetics of the ligand-induced monomerization were found to be significantly enhanced in the gas phase compared with the kinetics in solution, however. Ligand binding to the heme and the dissociation of the dimer in solution were also studied using energy transfer from a fluorescent probe to both heme groups of the protein. Comparison of ligand binding kinetics as observed with UV-vis spectroscopy with changes in fluorescence suggested that binding of one CO molecule per dimer could be sufficient for monomerization.

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Mechanism and Biological Role of Nitric Oxide Binding to Cytochrome c‘

Cited by 45 publications

References 20 publications

Regulation and Function of Cytochrome c ′ in Rhodobacter sphaeroides 2.4.3

Regulation and Function of Cytochrome c ′ in Rhodobacter sphaeroides 2.4.3

Molecular Basis for Nitric Oxide Dynamics and Affinity with Alcaligenes xylosoxidans Cytochrome c´

Ligand-induced monomerization of Allochromatium vinosum cytochrome c′ studied using native mass spectrometry and fluorescence resonance energy transfer

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