A Photolysis-Triggered Heme Ligand Switch in H93G Myoglobin

Franzen, Stefan; Bailey, James A.; Dyer, R. Brian; Woodruff, William H.; Hu, R.; Thomas, Melissa R.; Boxer, Steven G.

doi:10.1021/bi0023403

Cited by 22 publications

(63 citation statements)

References 37 publications

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“…3 indicate that the axial ligand of the heme iron is not the same in the H93G-CO and deoxy H93G species. This is in agreement with step-scan FTIR and saturation Raman data that indicate a dynamic ligand switch in H93G Mb [32]. The histidine that appears bound in the 8 ns photoproduct spectrum dissociates from the iron on a time scale < 5 ls.…”

Section: Ligand-free H93g Data Indicate a Ligand Switching Mechanismsupporting

confidence: 89%

“…This is certainly the case for H93G-*CO shown in Fig. 3, as it is known that a ligand switch occurs in H93G-*CO [32]. Of the ligands used in this study, it is likely that 2-methyl imidazole dissociates the most rapidly given the steric hindrance between the 2-methyl group of this ligand and the heme.…”

Section: R E S U L T Smentioning

confidence: 67%

“…Additionally, data are presented for the proximal cavity mutant in the absence of exogenous ligand (H93G). In this case the axial ligand trans to CO is one of the histidine residues located in the heme pocket of the globin [32]. Experimental comparison of the deoxy form for a ligand L [denoted H93G(L)] and the photolyzed CO form [denoted H93G(L)*CO] permits a comparison of the equilibrium deoxy state with that of a nonequilibrium state very close to that of the ligated species.…”

mentioning

confidence: 99%

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Proximal ligand motions in H93G myoglobin

Franzen

Peterson

Brown

et al. 2002

European Journal of Biochemistry

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Resonance Raman spectroscopy has been used to observe changes in the iron-ligand stretching frequency in photoproduct spectra of the proximal cavity mutant of myoglobin H93G. The measurements compare the deoxy ferrous state of the heme iron in H93G(L), where L is an exogenous imidazole ligand bound in the proximal cavity, to the photolyzed intermediate of H93G(L)*CO at 8 ns. There are significant differences in the frequencies of the iron-ligand axial out-of-plane mode m(Fe-L) in the photoproduct spectra depending on the nature of L for a series of methylsubstituted imidazoles. Further comparison was made with the proximal cavity mutant of myoglobin in the absence of exogenous ligand (H93G) and the photoproduct of the carbonmonoxy adduct of H93G (H93G-*CO). For this case, it has been shown that H 2 O is the axial (fifth) ligand to the heme iron in the deoxy form of H93G. The photoproduct of H93G-*CO is consistent with a transiently bound ligand proposed to be a histidine. The data presented here further substantiate the conclusion that a conformationally driven ligand switch exists in photolyzed H93G-*CO. The results suggest that ligand conformational changes in response to dynamic motions of the globin on the nanosecond and longer time scales are a general feature of the H93G proximal cavity mutant.Keywords: resonance Raman, heme, myoglobin, hemoglobin, ligand switch.Protein structural relaxation following heme photolysis has been studied in globins as a means to obtain information on structural intermediates following diatomic ligand photolysis. In hemoglobin (Hb), time-resolved spectroscopic studies have provided information on the time scale for transition from the six-coordinate R state to the fivecoordinate T-state [1][2][3]. The proximal cavity mutant of Hb has recently demonstrated the key role of the proximal histidine in the cooperativity of quaternary structure change in response to ligand binding [4]. Strain in the covalent bond to the heme iron of Hb can be monitored by following the shift in frequency of the iron-histidine axial mode, m(FeHis), by time-resolved resonance Raman spectroscopy [5]. In myoglobin (Mb), these studies have indicated a much smaller change in structure [6]: the observed frequency shift of the iron-histidine band is c. 1.6 cm )1 on the 8 ns time scale compared to 12 cm )1 in Hb. Nonetheless, this shift in the m(Fe-His) Raman band is significant because shifts in absorption bands (the time-dependent Soret band shift and band III shift) have been attributed to iron out-of-plane displacement that should also be coupled to m(Fe-His) [7][8][9][10]. A structural interpretation of these observable phenomena helps to bridge the gap between the extensive X-ray crystallography studies and the thermodynamic and kinetic data available for Mb [7,[11][12][13][14][15][16][17][18][19][20].Histidine-ligated heme enzymes have a surprisingly large range of functions. In peroxidase, a charge relay due to hydrogen bonding of the imidazole ring of histidine permits the formation of high valent iro...

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Section: Ligand-free H93g Data Indicate a Ligand Switching Mechanismsupporting

confidence: 89%

Section: R E S U L T Smentioning

confidence: 67%

mentioning

confidence: 99%

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Proximal ligand motions in H93G myoglobin

Franzen

Peterson

Brown

et al. 2002

European Journal of Biochemistry

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“…These proteins, like some mutant hemoproteins with a tyrosinate as single axial ligand, have I( 4 )/I( 3 ) intensity ratios in the 1-1.5 range. Such intensity ratios have also been reported for 5cHS hemoproteins with a coordinated hydroxide ion (32,33). No isotope shift was observed for H32A in H 2 18 O at pH 10.0 indicating that a hydroxide complex was not formed and that Tyr 75 was the most likely anionic oxygen heme ligand.…”

Section: Heme Iron Spin State and Coordinationsupporting

confidence: 76%

Role of the Iron Axial Ligands of Heme Carrier HasA in Heme Uptake and Release

Caillet‐Saguy

Piccioli

Turano

et al. 2012

Journal of Biological Chemistry

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“…Upon reduction with dithionite, the ν 4 oxidation-state marker band shifts to 1360 cm −1 while the ν 3 and ν 10 at 1471 and 1604 cm −1 , respectively, are indicative of a 5-coordinate high-spin configuration (Figure 7). Binding of CO up-shifts these frequencies (ν 4 at 1374, ν 3 at 1503, and ν 10 at 1638 cm −1 ) and results in the detection of a ν (Fe-CO) at 533 cm −1 (Figure 8), which is characteristic of heme-carbonyl complexes with a weak or no proximal ligand (24,(26)(27)(28). Figure 9 shows the electrochemistry of wild-type Dap1p as evaluated using UV-Vis spectroelectrochemistry.…”

Section: Rr Characterization Of Dap1pmentioning

confidence: 99%

Measurement of the Heme Affinity for Yeast Dap1p, and Its Importance in Cellular Function

et al. 2007

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Current studies on the Saccharomyces cerevisiae protein Dap1p have demonstrated a heme related function within the ergosterol biosynthetic pathway. Here we present data to further the understanding of the role of heme in the proper biological functioning of Dap1p in cellular processes. Firstly, we examined the role of Dap1p in stabilizing the P 450 enzyme, Erg11p, a key protein involved with facilitating ergosterol biosynthesis. Our data indicates that the absence of Dap1p does not affect Erg11p mRNA or protein expression levels, nor the protein degradation rates. Secondly, in order to probe the role of heme in the biological functioning of Dap1p, we measured ferric and ferrous heme binding affinities for Dap1p and the mutant Dap1p Y138F

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A Photolysis-Triggered Heme Ligand Switch in H93G Myoglobin

Cited by 22 publications

References 37 publications

Proximal ligand motions in H93G myoglobin

Proximal ligand motions in H93G myoglobin

Role of the Iron Axial Ligands of Heme Carrier HasA in Heme Uptake and Release

Measurement of the Heme Affinity for Yeast Dap1p, and Its Importance in Cellular Function

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