Catalytic Efficiency of Basidiomycete Laccases: Redox Potential versus Substrate-Binding Pocket Structure

Abstract

Laccases are copper-containing oxidases that catalyze a one-electron abstraction from various phenolic and non-phenolic compounds with concomitant reduction of molecular oxygen to water. It is well-known that laccases from various sources have different substrate specificities, but it is not completely clear what exactly provides these differences. The purpose of this work was to study the features of the substrate specificity of four laccases from basidiomycete fungi Trametes hirsuta, Coriolopsis caperata, Antrodiella faginea, and Steccherinum murashkinskyi, which have different redox potentials of the T1 copper center and a different structure of substrate-binding pockets. Enzyme activity toward 20 monophenolic substances and 4 phenolic dyes was measured spectrophotometrically. The kinetic parameters of oxidation of four lignans and lignan-like substrates were determined by monitoring of the oxygen consumption. For the oxidation of the high redox potential (>700 mV) monophenolic substrates and almost all large substrates, such as phenolic dyes and lignans, the redox potential difference between the enzyme and the substrate (∆E) played the defining role. For the low redox potential monophenolic substrates, ∆E did not directly influence the laccase activity. Also, in the special cases, the structure of the large substrates, such as dyes and lignans, as well as some structural features of the laccases (flexibility of the substrate-binding pocket loops and some amino acid residues in the key positions) affected the resulting catalytic efficiency.

White-rot basidiomycetes Junghuhnia nitida and Steccherinum bourdotii: Oxidative potential and laccase properties in comparison with Trametes hirsuta and Coriolopsis caperata

“…It is believed that the catalytic efficiency of different substrates oxidation is correlated with a redox potential difference (Δ E 0 ) between a substrate and a laccase [ 50 ]. However, the catalytic efficiency depends not only on the redox-potential difference but also on the steric features like shape of the substrate and shape and structure of the substrate-binding pocket of the laccase [ 51 – 53 ]. In our case, despite their middle redox potential, SbL and JnL could oxidize a broad range of substrates, including monoaromatic phenols (pyrocatechol, 2,6-DMP, guaiacol, sinapic and gallic acids), complex phenol (syringaldazine), natural dilignan (pinoresinol) and the non-phenolic heterocyclic compound ABTS, like high-redox potential laccases ThL and CcL ( Table 3 ).…”

Laccases: structure, function, and potential application in water bioremediation

“…The general three-domain structure of laccases is maintained in different species, with the loops protruding the cupredoxin domains being the most conspicuous difference [111, 151], as well as the form and by consequence, the selectivity at the substrate binding site [152]. More subtle differences are situated in the axial position of the T1 copper atom, causing the span of E °s from 400 mV in plant and bacterial laccases to approximately 800 mV in the majority of fungal types [22, 139, 153]. In Fig.…”

Oxidative Transformations of Lignans

“…They play a key role in the dimerization of 4-hydroxycinnamic acids in the biosyntheses of natural lignans [22,169]. Lignans have also been used as substrates in laccase activity studies [170,171]. Laccase oxidations of lignans baring guaiacyl groups have led to efficient polymerization [172,173,174].…”