Reduction thermodynamics of the T1 Cu site in plant and fungal laccases

Abstract

The thermodynamic parameters for reduction of the type-1 (T1) copper site in Rhus vernicifera and Trametes versicolor laccases and for the derivative of the former protein from which the type-2 copper has been selectively removed (T2D) have been determined with UV-vis spectroelectrochemistry. In all cases, the enthalpic term turns out to be the main determinant of the Eo' of the T1 site. Also the difference between the reduction potentials of the two laccases is enthalpy-based and reflects differences in the coordination features of the T1 sites and their protein environment. The T1 sites in native R. vernicifera laccase and its T2D derivative show the same Eo', as a result of compensatory differences in the reduction thermodynamics. This suggests that removal of the type-2 (T2) copper results in modification of the reduction-induced solvent reorganization effects, with no influence in the structure of the multicopper protein site. This conclusion is supported by NMR data recorded on the native, the T2D, and Hg-substituted T1 derivatives of R. vernicifera laccase, which show that the T1 and T2/T3 sites are largely noninteracting.

Laccase Redox Potentials: pH Dependence and Mutants, a QM/MM Study

“…Met-variants of MCOs tend to exhibit a slightly lower RP (by about 0.09 to 0.1 V) than MCOs with Phe. 19,51,52 Because both residues are neutral, this is a more subtle effect than the protonation/deprotonation equilibria studied above. On the other hand, these residues are much closer to the T1 site, so close in fact that both are included in the respective QM regions.…”

Four-electron reduction of O2 over multiple CuI centers: Quantum theory

“…Linear Gibbs energy relationships are common in chemistry. Specific support in the present context is in the recent experimental work on the reduction thermodynamics of the T1 Cu site that showed the enthalpic term is the main determinant of the reversible potential [37].…”

Disruption of the H-bond network in the main access channel of catalase–peroxidase modulates enthalpy and entropy of Fe(III) reduction

“…Since reduction thermodynamics for metalloproteins in aqueous solution are deeply affected by solvent reorganization phenomena [21][22][23][24][25][44][45][46], the thermodynamic data listed in Table 1, as such, cannot be used to extract information on mutation-induced proteinbased effects on the thermodynamics of Fe(III) to Fe(II) reduction. In particular, it is worthy of note that for all the present KatG variants the mutation-induced changes in ΔH°′ rc and ΔS°′ rc are much larger than the corresponding changes in ΔG°′ rc , and therefore in E°′ (Table 1).…”

“…Since changes in conformational degrees of freedom of the polypeptide chain upon reduction can be neglected (see above) [17][18][19][20][21][22][23][24] and solvent reorganization effects mainly contribute to ΔS°′ rc , the increase in solvent ordering upon formation of ferrous KatG can be related to its channel architecture and H-bond network. In fact, KatGs have a buried active site and a more defined water matrix on the distal side compared to monofunctional peroxidases [12,49,55].…”

“…All experiments were carried out in a homemade OTTLE cell [17][18][19][20][21][22][23][24]. The three-electrode configuration consisted of a gold minigrid working electrode (Buckbee-Mears, Chicago, IL), a homemade Ag/ AgCl/KCl sat microreference electrode, separated from the working solution by a Vycor set, and a platinum wire as the counter electrode.…”