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Theoretical study of the structural and spectroscopic properties of stellacyanin

De Kerpel, Jan O A; Pierloot, Kristine; Ryde, Ulf LU and Roos, Björn O. LU (1998) In Journal of Physical Chemistry B 102(23). p.4638-4647
Abstract

The electronic spectrum of the azurin Met121Gln mutant, a model of the blue copper protein stellacyanin, has been studied by ab initio multiconfigurational second-order perturbation theory (the CASPT2 method), including the effect of the protein and solvent by point charges. The six lowest electronic transitions have been calculated and assigned with an error of less than 2400 cm-1. The ground-state singly occupied orbital is found to be a predominantly π antibonding orbital involving Cu3d and Scys3pπ. However, it also contains a significant amount (18%) of Cu-Scys σ antibonding character. This σ interaction is responsible for the appearance in the absorption spectrum of a band at 460 nm, with... (More)

The electronic spectrum of the azurin Met121Gln mutant, a model of the blue copper protein stellacyanin, has been studied by ab initio multiconfigurational second-order perturbation theory (the CASPT2 method), including the effect of the protein and solvent by point charges. The six lowest electronic transitions have been calculated and assigned with an error of less than 2400 cm-1. The ground-state singly occupied orbital is found to be a predominantly π antibonding orbital involving Cu3d and Scys3pπ. However, it also contains a significant amount (18%) of Cu-Scys σ antibonding character. This σ interaction is responsible for the appearance in the absorption spectrum of a band at 460 nm, with a significantly higher intensity than observed for other, axial, type 1 copper proteins (i.e., plastocyanin or azurin). The π-σ mixing is caused by the axial glutamine ligand binding at a much shorter distance to copper than the corresponding methionine ligand in the normal blue copper proteins. This explains why, based on its spectral properties, stellacyanin is classified among the rhombic type 1 copper proteins, although its structure is clearly trigonal, as it is for the axial proteins. Calculations have also been performed on structures where the glutamine model coordinates to the copper ion via the deprotonated N atom instead of the O atom. However, the resulting transition energies do not resemble the experimental spectrum obtained at normal or elevated pH. Thus, the results do not confirm the suggestion that the coordinating atom of glutamine changes at high pH.

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Contribution to journal
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published
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in
Journal of Physical Chemistry B
volume
102
issue
23
pages
10 pages
publisher
The American Chemical Society
external identifiers
  • scopus:0000288328
ISSN
1089-5647
DOI
10.1021/jp980455z
language
English
LU publication?
yes
id
f488c41c-abd2-4427-aded-a8fc7577e2aa
date added to LUP
2017-02-04 11:37:39
date last changed
2017-08-27 06:34:48
@article{f488c41c-abd2-4427-aded-a8fc7577e2aa,
  abstract     = {<p>The electronic spectrum of the azurin Met121Gln mutant, a model of the blue copper protein stellacyanin, has been studied by ab initio multiconfigurational second-order perturbation theory (the CASPT2 method), including the effect of the protein and solvent by point charges. The six lowest electronic transitions have been calculated and assigned with an error of less than 2400 cm<sup>-1</sup>. The ground-state singly occupied orbital is found to be a predominantly π antibonding orbital involving Cu3d and S<sub>cys</sub>3p<sub>π</sub>. However, it also contains a significant amount (18%) of Cu-S<sub>cys</sub> σ antibonding character. This σ interaction is responsible for the appearance in the absorption spectrum of a band at 460 nm, with a significantly higher intensity than observed for other, axial, type 1 copper proteins (i.e., plastocyanin or azurin). The π-σ mixing is caused by the axial glutamine ligand binding at a much shorter distance to copper than the corresponding methionine ligand in the normal blue copper proteins. This explains why, based on its spectral properties, stellacyanin is classified among the rhombic type 1 copper proteins, although its structure is clearly trigonal, as it is for the axial proteins. Calculations have also been performed on structures where the glutamine model coordinates to the copper ion via the deprotonated N<sup>∈</sup> atom instead of the O<sup>∈</sup> atom. However, the resulting transition energies do not resemble the experimental spectrum obtained at normal or elevated pH. Thus, the results do not confirm the suggestion that the coordinating atom of glutamine changes at high pH.</p>},
  author       = {De Kerpel, Jan O A and Pierloot, Kristine and Ryde, Ulf and Roos, Björn O.},
  issn         = {1089-5647},
  language     = {eng},
  month        = {06},
  number       = {23},
  pages        = {4638--4647},
  publisher    = {The American Chemical Society},
  series       = {Journal of Physical Chemistry B},
  title        = {Theoretical study of the structural and spectroscopic properties of stellacyanin},
  url          = {http://dx.doi.org/10.1021/jp980455z},
  volume       = {102},
  year         = {1998},
}