Infrared spectroscopic studies of carbonyl horseradish peroxidases

The affinity and reactivity of the gaseous molecules CO, NO and O2 (XO) in heme protein adducts are controlled by secondary interactions, especially by H-bonds donated from distal protein residues. Vibrational spectroscopy, supported by DFT modeling, has revealed that for NO and O2, but not for CO, a critical issue is whether the H-bond is donated to the outer or inner atom of the bound diatomic ligand. DFT modeling shows that bound NO and O2 are ambidentate, both atoms separately acting as H-bond acceptors. This is not the case for CO, whose π* orbital acts as a delocalized H-bond acceptor. Vibrational spectra of heme-XO adducts reveal a general pattern of backbonding variations, marked by families of negative correlations between frequencies associated with Fe-X and X-O bond stretches. For heme-CO adducts, H-bonding increases backbonding, the νFeX/νXO points moving up the backbonding correlation established with model compounds. For NO and O2 adducts, however, increased backbonding is only observed when the outer atom is the H-bond acceptor. H-bonding to the inner (X) atom instead produces a positive νFeX/νXO correlation. This effect can be reproduced by DFT modeling. Its mechanism is polarization of the sp2 orbital on the X atom, on the back side of the bent FeXO unit, drawing electrons from both the Fe-X and X-O bonds and weakening them together. Thus, the positioning of H-bond donors in the protein differentially affects bonding and reactivity in heme adducts of NO and O2.

show abstract

“…However, νCO vibrations occur in an uncluttered region of the spectrum, and can be monitored via infrared spectroscopy. [22–27]…”

Section: Backbonding Pattern Of Vibrational Frequenciesmentioning

confidence: 99%

Ambidentate H-bonding of NO and O2 in heme proteins

Spiro

Soldatova

2012

Journal of Inorganic Biochemistry

View full text Add to dashboard Cite

show abstract

“…The reduction in the peak enthalpy reflects the reduced hindrance experienced by the ligand in rebinding to the glycine mutant; the reduction in the preexponential can be attributed to the increased entropy of the mutant-ligand system in state B owing to the larger distal pocket in the glycine mutant (24). In native Mb the distal histidine affects binding both sterically and electrostatically (6,(25)(26)(27)(28)(29)(30). Comparing the CO (Table 1).…”

Section: N(t T) = Aa(t T)/aa(0 T)mentioning

confidence: 99%

Ligand binding to synthetic mutant myoglobin (His-E7----Gly): role of the distal histidine.

Braunstein

Ansari

Berendzen

et al. 1988

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Low-temperature flash photolysis with IR and visible spectroscopy was used to probe the influence of the distal histidine His-64(E7) of sperm-whale myoglobin (Mb) on the orientation of bound carbon monoxide (CO) and on the kinetics of CO rebinding. The synthesis and high-level expression of a sperm-whale myoglobin gene in Escherichia coli permits the efficient substitution of the distal histidine through site-directed mutagenesis. Substitution of His-E7 with glycine [GlyE7]Mb at 10 K reveals the bound CO to be oriented at an angle of a = 20°± 2°with respect to the heme normal. Flash photolysis data from 10 to 300 K provide evidence for a larger distal pocket and a smaller enthalpy barrier (by =4 kJ/mol) for [GlyE7JMbCO as compared with wild-type MbCO. These results reinforce the notion that the dominant control of the binding step at the heme iron comes from the proximal side through the protein structure.The relation between macromolecular structure and function is one of the most intriguing problems in molecular biology. In the oxygen storage and transport proteins, myoglobin (Mb) and hemoglobin (Hb), a central issue is the role of the protein structure in the selective binding of atmospheric 02 versus

show abstract

“…These data are supportive of a hydrogen-bonding interaction at the lower pH, which is perhaps not present at the higher pH, so that more nearly linear Fe-C--0 bonding results. Such an interaction has also been proposed to account for the pH-dependent changes in one of the two vco values observed in the case of H R P C O (Barlow et al, 1976). Support for a more linear bond between the heme iron and carbon monoxide in the absence of camphor, at least for that portion of the enzyme giving rise to the vco 1962 cm-], is derived from studies with several H b carbonyls, including H b ME^^^^ and H b Zurich in which structural changes adjacent to the heme iron have been suggested to cause an opening of the crevice, thereby allowing the bent Fe-C-0 to become more neakly linear, as expressed by a shift in vco to higher wavenumbers (Table I).…”

Section: Phmentioning

confidence: 99%

An infrared spectroscopic study of carbon monoxide bonding to ferrous cytochrome P-450

O'Keefe¹,

Ebel²,

Peterson³

et al. 1978

Biochemistry

View full text Add to dashboard Cite

Ferrous-carbonyl complexes of the soluble Pseudomonas putida cytochrome P-450,,, and a denatured form (P-420) of this enzyme, as well as cytochromes P-450 and P-448 in liver microsomes from rats pretreated with phenobarbital and 3-methylcholanthrene, have been studied by infrared spectroscopy. The FeCO bonding was examined in order to probe the spatial relationship between the dioxygen-and substrate-binding sites and to determine whether the presence of a unique axial ligand bound trans to carbon monoxide could be responsible for the red-shifted Soret absorbance band maximum at 450 nm. The d-camphor(K+)-bound cytochrome P-450,,, yielded a single infrared absorbance band for the heme-bound carbonyl (uc-, 1940 cm-') having a bandwidth a t half-height ( A v l p ) of 13 ern-', while the camphor-free enzyme gave rise to two stretching frequencies of equal area a t 1963 and 1942 cm-' ( A u l / 2 11-12 and 19-21 cm-', respectively). Addition of d-camphor and a monovalent metal ion (K+) to the camphor-free ferrous carbonyl-enzyme converted the infrared spectrum back to that of the original camphor-bound enzyme. The area of the 1940-cm-I band was found to equal that of the combined areas of the 1963-and 1942-cm-l bands. Conversion of the native enzyme to a denatured form (P-420) yielded a w-, 1966 cm-' with A u l p 23 1 nfrared spectroscopy is a powerful technique for probing the oxygen binding site of heme proteins. Carbon monoxide has been the ligand of choice for such studies because the C-0 stretching frequency is much more easily observed in aqueous media than is that of the 0-0 stretching frequency (Maxwell and Caughey, 1978) and because its substitution for 0 2 is assumed to leave the structure of the protein unaltered. The infrared stretching frequency is related to the C-0 bond energy which is very sensitive to differences in both bond type and environment. The present study was initiated to directly probe, by infrared spectroscopy, the dioxygen-binding site of cyto-

show abstract

Infrared spectroscopic studies of carbonyl horseradish peroxidases

Cited by 81 publications

References 13 publications

Ambidentate H-bonding of NO and O2 in heme proteins

Ambidentate H-bonding of NO and O2 in heme proteins

Ligand binding to synthetic mutant myoglobin (His-E7----Gly): role of the distal histidine.

An infrared spectroscopic study of carbon monoxide bonding to ferrous cytochrome P-450

Contact Info

Product

Resources

About