Electronic structure of the oxidized and reduced blue copper sites: contributions to the electron transfer pathway, reduction potential, and geometry

Solomon, Edward I.; Penfield, Kevin W.; Gewirth, Andrew A.; Lowery, Michael D.; Shadle, Susan E.; Guckert, Jeffrey A.; LaCroix, Louis B.

doi:10.1016/0020-1693(95)04893-6

Cited by 123 publications

(162 citation statements)

References 36 publications

Supporting

Mentioning

151

Contrasting

Order By: Relevance

“…The characteristics observed for the excited-state deactivation process occurring in POXC suggest that its T1 Cu site characteristics are different from those of the other proteins investigated by ultrafast resonant pump-probe spectroscopy. This well correlates with the hypothesis that POXC T1 Cu is strongly coordinated to only the three ligands constituting the common T1 Cu ligand set, i.e., thiolate sulfur of a cysteine residue and the imidazole nitrogens of two histidine residues, and thus T1 site features a trigonal geometry [3,10,28]. In fact in all of the copper-containing proteins so far investigated by ultrafast resonant pump-probe spectroscopy the T1 copper is ligated to at least four ligands.…”

Section: Resultssupporting

confidence: 80%

Ultrafast excited-state charge-transfer dynamics in laccase type I copper site

Delfino

Viola

Cerullo

et al. 2015

Biophysical Chemistry

View full text Add to dashboard Cite

• T1Cu MLCT in POXC is described by ultrafast pump-probe spectroscopy • The first step of the charge-transfer in POXC occurs within 375 fs • Ground-state coherent oscillations are compared to Resonance Raman features • The trigonal T1 Cu site geometry hypothesized for POXC is confirmed by the results G R A P H I C A L A B S T R A C Ta b s t r a c t a r t i c l e i n f o Femtosecond pump-probe spectroscopy was used to investigate the excited state dynamics of the T1 copper site of laccase from Pleurotus ostreatus, by exciting its 600 nm charge transfer band with a 15-fs pulse and probing over a broad range in the visible region. The decay of the pump-induced ground-state bleaching occurs in a single step and is modulated by clearly visible oscillations. Global analysis of the two-dimensional differential transmission map shows that the excited state exponentially decays with a time constant of 375 fs, thus featuring a decay rate slower than those occurring in quite all the investigated T1 copper site proteins. The ultrashort pump pulse induces a vibrational coherence in the protein, which is mainly assigned to ground state activity, as expected in a system with fast excited state decay. Vibrational features are discussed also in comparison with the traditional resonance Raman spectrum of the enzyme. The results indicate that both excited state dynamics and vibrational modes associated with the T1 Cu laccase charge transfer have main characteristics similar to those of all the T1 copper site-containing proteins. On the other hand, the differences observed for laccase from P. ostreatus further confirm the peculiar hypothesized trigonal T1 Cu site geometry.

show abstract

Section: Resultssupporting

confidence: 80%

Ultrafast excited-state charge-transfer dynamics in laccase type I copper site

Delfino

Viola

Cerullo

et al. 2015

Biophysical Chemistry

View full text Add to dashboard Cite

show abstract

“…(3,(10)(11)(12)(13) First, the spectral features resulting from the d9 oxidized blue Cu ground state wavefunction are well understood. (3,10) This half-occupied orbital participates in electron transfer which is facilitated by a high degree of covalency anisotropically distributed along one Cu-ligand bond (the cysteine).…”

Section: Introductionmentioning

confidence: 99%

Geometric and Electronic Structure Contributions to Function in Bioinorganic Chemistry: Active Sites in Non-Heme Iron Enzymes

Solomon

2001

Inorg. Chem.

Self Cite

View full text Add to dashboard Cite

Abstract:The blue copper site has a unique electronic structure which contributes to its electron transfer function and is reflected in unique spectral properties. The HOMO in the oxidized blue Cu site exhibits high anisotripic covalency which enhances intra-and inter-protein electron transfer rates. The electronic structure of the reduced dlo blue Cu centers is developed using a combination of variable energy photoelectron spectroscopy and density functional calculations. These studies establish the change in electronic structure that occurs upon oxidation of the blue Cu center and permit an evaluation of whether the reduced geometry is imposed on the oxidized site by the protein (i.e. the entatidrack state). Studies of the perturbed blue Cu site in nitrite reductase demonstrate that a tetragonal distortion is the origin of the perturbed spectral features of this site. This distortion derives from a Jahn-Teller force along an -E(u) mode not present in the classic blue copper proteins and reflects differences in protein contributions to active site structure.

show abstract

“…1B) (8)(9)(10)(11). Both sites carry out rapid, efficient longrange ET with rates on the order of 10 3 -10 5 s −1 (12,13).…”

mentioning

confidence: 99%

Axial interactions in the mixed-valent Cu _A active site and role of the axial methionine in electron transfer

Tsai

Hadt

Marshall

et al. 2013

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

Self Cite

View full text Add to dashboard Cite

Within Cu-containing electron transfer active sites, the role of the axial ligand in type 1 sites is well defined, yet its role in the binuclear mixed-valent Cu A sites is less clear. Recently, the mutation of the axial Met to Leu in a Cu A site engineered into azurin (Cu A Az) was found to have a limited effect on E 0 relative to this mutation in blue copper (BC). Detailed low-temperature absorption and magnetic circular dichroism, resonance Raman, and electron paramagnetic resonance studies on Cu A Az (WT) and its M123X (X = Q, L, H) axial ligand variants indicated stronger axial ligation in M123L/H. Spectroscopically validated density functional theory calculations show that the smaller ΔE 0 is attributed to H 2 O coordination to the Cu center in the M123L mutant in Cu A but not in the equivalent BC variant. The comparable stabilization energy of the oxidized over the reduced state in Cu A and BC (Cu A ∼ 180 mV; BC ∼ 250 mV) indicates that the S(Met) influences E 0 similarly in both. Electron delocalization over two Cu centers in Cu A was found to minimize the Jahn-Teller distortion induced by the axial Met ligand and lower the inner-sphere reorganization energy. The Cu-S(Met) bond in oxidized Cu A is weak (5.2 kcal/ mol) but energetically similar to that of BC, which demonstrates that the protein matrix also serves an entatic role in keeping the Met bound to the active site to tune down E 0 while maintaining a low reorganization energy required for rapid electron transfer under physiological conditions. spectroscopy | reduction potential | energy transduction pathway L ong-range electron transfer (ET) is vital to a wide range of biological processes, including two key energy transduction pathways essential for life: H 2 O oxidation in photosynthesis and O 2 reduction in respiration (1, 2). Nature has adapted a conserved cupredoxin fold motif (i.e., the Greek-key β barrel) to construct two evolutionarily linked, but structurally distinct Cucontaining ET proteins (3-5). These are the mononuclear type 1 (T1) or blue copper (BC) and binuclear purple Cu A proteins. The first coordination sphere of the classic BC sites [e.g., plastocyanin (Pc) and azurin (Az)] consists of a trigonally distorted tetrahedral environment where Cu resides in an equatorial plane formed by one S(Cys) and two N(His) ligands and has an axial S (Met) ligand (Fig. 1A) (Fig. 1B) (8-11). Both sites carry out rapid, efficient longrange ET with rates on the order of 10 3 -10 5 s −1 (12, 13).Although BC proteins use a Cu + /Cu 2+ redox couple, the binuclear Cu A sites use a (Cu 1+ -Cu 1+ )/(Cu 1.5+ -Cu 1.5+ ) redox cycle. The oxidized form of Cu A is mixed-valent (MV), with a highly covalent Cu 2 S 2 core that gives rise to its unique spectroscopic features. The unpaired electron is fully delocalized over the two Cu centers and exhibits a characteristic seven-line 63,65 Cu hyperfine splitting pattern in electron paramagnetic resonance (EPR) spectroscopy (14, 15). Maintaining valence delocalization even in the presence of a low symmetry protein ...

show abstract

Electronic structure of the oxidized and reduced blue copper sites: contributions to the electron transfer pathway, reduction potential, and geometry

Cited by 123 publications

References 36 publications

Ultrafast excited-state charge-transfer dynamics in laccase type I copper site

Ultrafast excited-state charge-transfer dynamics in laccase type I copper site

Geometric and Electronic Structure Contributions to Function in Bioinorganic Chemistry: Active Sites in Non-Heme Iron Enzymes

Axial interactions in the mixed-valent Cu _A active site and role of the axial methionine in electron transfer

Contact Info

Product

Resources

About

Electronic structure of the oxidized and reduced blue copper sites: contributions to the electron transfer pathway, reduction potential, and geometry

Cited by 123 publications

References 36 publications

Ultrafast excited-state charge-transfer dynamics in laccase type I copper site

Ultrafast excited-state charge-transfer dynamics in laccase type I copper site

Geometric and Electronic Structure Contributions to Function in Bioinorganic Chemistry: Active Sites in Non-Heme Iron Enzymes

Axial interactions in the mixed-valent Cu A active site and role of the axial methionine in electron transfer

Contact Info

Product

Resources

About

Axial interactions in the mixed-valent Cu _A active site and role of the axial methionine in electron transfer