Carbon Monoxide Complex of Cytochrome b5 at Acidic pH

Hirota, Shun; Kishi, Mamiko; Yamauchi, Osamu; Wang, Yunhua; Huang, Zhong‐Xian

doi:10.1006/bbrc.2001.4544

Cited by 5 publications

(4 citation statements)

References 26 publications

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“…The studies presented herein suggest that Pro 2 serves as the distal ligand in CooA because it is more weakly bound to heme than the proximal histidine ligand and, therefore, can be more readily displaced by CO. A weak ligand, such as an N-terminal amine, is important to enable distal CO binding to the CooA heme, as evidenced by the fact that CO binding is disrupted when the stronger His 116 ligand replaces Pro 2 as the distal ligand in L116H CooA. Prior studies of CO binding to cytochrome b 5 demonstrated that the strength of the metal−ligand bond governs the ability of a low-spin 6-coordinate heme to bind CO ( , ). Cytochrome b 5 , which contains a His 39 /His 63 coordinated heme, does not react appreciably with CO at higher pH values.…”

Section: Discussionmentioning

confidence: 99%

“…Cytochrome b 5 , which contains a His 39 /His 63 coordinated heme, does not react appreciably with CO at higher pH values. At pH 3.5, however, cytochrome b 5 reacts with CO slowly and completely over ∼40 min (57). Formation of the Fe(II)-CO adduct at this low pH correlates with the onset of protein denaturation, which presumably weakens the Fe-His bond and facilitates ligand displacement.…”

Section: Wt Cooa and The N-terminal Variants Utilize The N-terminal A...mentioning

confidence: 97%

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Investigation of the Role of the N-Terminal Proline, the Distal Heme Ligand in the CO Sensor CooA

et al. 2004

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A unique feature of CooA, a heme-containing transcription factor, is that the N-terminal proline is the distal heme ligand in the ferrous state, and this ligand is displaced upon CO binding. To investigate the importance of Pro(2) in CO-dependent DNA binding, several CooA variants that alter N-terminal ligation were characterized. Electronic absorption, electron paramagnetic resonance, and magnetic circular dichroism spectra of these variants provide the most definitive evidence that Pro(2) is the distal ligand in Fe(III) CooA. Furthermore, the functional and spectroscopic properties of these proteins depended on whether a weak ligand occupied the distal heme coordination site: for CooA variants in which distal coordination is disrupted, the DNA-binding affinities and Fe(II)-CO spectral properties showed an unexpected dependence on the order of CO addition and heme reduction. If N-terminal variant samples were incubated with CO before the heme was reduced, the proteins displayed DNA-binding affinities and Fe(II)-CO spectral characteristics similar to those of wild-type (WT) CooA. However, if the same samples were incubated with CO after the heme was reduced, the extent of functional and spectral similarity to WT CooA negatively correlated with the amount of high-spin heme present in the ferric state. From these data, it was inferred that the absence of a distal heme ligand in the ferric state prevents WT-like CO binding to the ferrous state, and it was hypothesized that correct CO binding is inhibited by the collapse of the distal heme pocket upon reduction. Together with the observation that L116H CooA, a variant in which His(116) replaces Pro(2) as the distal heme ligand, binds CO more slowly than WT CooA, these data indicate that the presence of a weak distal heme ligand, not specifically ligation by the N-terminal proline, is crucial for proper function. The role of Pro(2) in CooA is apparently to direct CO to bind on the distal side of heme and to help maintain the integrity of the distal heme pocket during the redox-mediated ligand switch.

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Section: Discussionmentioning

confidence: 99%

Section: Wt Cooa and The N-terminal Variants Utilize The N-terminal A...mentioning

confidence: 97%

Investigation of the Role of the N-Terminal Proline, the Distal Heme Ligand in the CO Sensor CooA

et al. 2004

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“…If Hess meant cytochrome b5 (of the erythrocyte methaemoglobin reduction pathway) instead of cytochrome c5 , , that also would not explain the observations. CO is not expected to inhibit cytochrome b5 as it is not known to bind CO under non-denaturing conditions [4]. Even if methaemoglobin reduction were inhibited by CO, stabilization of haemoglobin by CO as well as the anaerobic condition would greatly reduce the rate of haemoglobin oxidation.…”

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confidence: 99%

Storage of red blood cells under anaerobic conditions: reply

Yoshida

AuBuchon

2007

Vox Sanguinis

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“…This rigid structure would not accommodate the large coordinated His side chain movement that is essential for reversible coordination in the nsHb mechanism. Furthermore, modifications that allow ligand binding to occur in cyt b 5 (Rodriguez and Rivera, 1998;Ihara et al, 2000;Hirota et al, 2001) result in increased heme loss since cyt b 5 relies heavily on axial coordination for heme retention, due to heme cavity polarity and solvent exposure Falzone et al, 1996;Falzone et al, 2001;Wang et al, 2003). Therefore, it is evident that the structure of nsHb is specially suited to disrupt His coordination, allowing the flexibility in the E-helix required for a conformation shift that stabilizes the resulting pentacoordinate protein.…”

Section: A Mechanism To Achieve Reversible Ligand Bindingmentioning

confidence: 99%

Structural characterization of ligand binding in hexacoordinate hemoglobins

Hoy

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Carbon Monoxide Complex of Cytochrome b5 at Acidic pH

Cited by 5 publications

References 26 publications

Investigation of the Role of the N-Terminal Proline, the Distal Heme Ligand in the CO Sensor CooA

Investigation of the Role of the N-Terminal Proline, the Distal Heme Ligand in the CO Sensor CooA

Storage of red blood cells under anaerobic conditions: reply

Structural characterization of ligand binding in hexacoordinate hemoglobins

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