LACCASES: CHARACTERISTICS, STRUCTURE, FUNCTIONS - SCIENCE - 2025

The laccases, p- diphenol: oxidoreductases dioxygen-benzenediol oxygen oxidoreductases, or, are enzymes belonging to the group of enzymes called oxidases "blue copper oxidases".

They exist in higher plants, in some insects, in bacteria and in practically all fungi that have been studied; its characteristic blue color is the product of four copper atoms attached to the molecule at its catalytic site.

Graphic representation of the molecular structure of a Laccase enzyme (Source: Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute via Wikimedia Commons)

These enzymes were described by Yoshida et al. In 1883, when they studied the resin of the Japanese Rhus vernicifera tree or "lacquer tree", where it was determined that their main function was to catalyze polymerization and depolymerization reactions of compounds.

Much later it was discovered that, in fungi, these proteins with enzymatic activity have specific functions in the mechanisms of removal of toxic phenols from the environment where they grow, while in plants they are involved in synthetic processes such as lignification.

Scientific advances regarding the study of these enzymes allowed their use at an industrial level, where their catalytic capacity has been used, especially in the contexts of bioremediation, textiles, in the removal of dyes applied to textiles, in the paper industry, among others.

The main reasons why laccases are so interesting from an industrial point of view have to do with the fact that their oxidation reactions simply involve the reduction of molecular oxygen and the production of water as a secondary element.

characteristics

Laccase enzymes can be secreted or found in the intracellular region, but this depends on the organism being studied. Despite this, most of the enzymes analyzed (with the exception of some proteins from certain fungi and insects) are extracellular proteins.

Distribution

These enzymes, as discussed above, are predominantly found in fungi, higher plants, bacteria, and some species of insects.

Among the plants where its existence has been demonstrated are apple trees, asparagus, potatoes, pears, mangoes, peaches, pines, plums, among others. Laccase-expressing insects belong mainly to the genera Bombyx, Calliphora, Diploptera, Drosophila, Musca, Papilio, Rhodnius, and others.

Fungi are the organisms from which the greatest number and variety of laccases have been isolated and studied, and these enzymes are present in both ascomycetes and deuteromycetes and basidiomycetes.

Catalysis

The reaction catalyzed by laccases consists of the monoelectronic oxidation of a substrate molecule, which can belong to the group of phenols, aromatic compounds or aliphatic amines, to its corresponding reactive radical.

The result of the catalytic reaction is the reduction of one oxygen molecule to two water molecules and the oxidation, at the same time, of four substrate molecules to produce four reactive free radicals.

Intermediate free radicals can join and form dimers, oligomers or polymers, thus laccases are said to catalyze polymerization and "depolymerization" reactions.

Structure

Laccases are glycoproteins, that is, they are proteins that have oligosaccharide residues covalently linked to the polypeptide chain, and these represent between 10 and 50% of the total weight of the molecule (in plant enzymes the percentage may be a little higher).

The carbohydrate portion of this type of protein contains monosaccharides such as glucose, mannose, galactose, fucose, arabinose, and some hexosamines, and glycosylation is thought to play important roles in secretion, proteolytic susceptibility, activity, copper retention, and the thermal stability of the protein.

These enzymes are generally found in nature as monomers or homodimers, and the molecular weight of each monomer can vary between 60 and 100 kDa.

The catalytic center of laccases is made up of four copper (Cu) atoms, which give the molecule in general a blue color due to the electronic absorption that takes place in the copper-copper (Cu-Cu) bonds.

Vegetable laccases have isoelectric points with values ​​close to 9 (quite basic), while fungal enzymes are between isoelectric points of 3 and 7 (so they are enzymes that work in acidic conditions).

Isoenzymes

Many laccase-producing fungi also have laccase isoforms, which are encoded by the same gene or by different genes. These isoenzymes differ from one another mainly in terms of their stability, their optimal pH and temperature for catalyzing, and their affinity for different types of substrate.

Under certain conditions, these isoenzymes can have different physiological functions, but this depends on the species or the condition in which it lives.

Features

Some researchers have shown that laccases are involved in the "sclerotization" of the cuticle in insects and the assembly of spores resistant to ultraviolet light in microorganisms of the genus Bacillus.

In plants

In plant organisms, laccases participate in the formation of the cell wall, in the processes of lignification and "delignification" (loss or disintegration of lignin); and furthermore, they have been related to the detoxification of tissues through the oxidation of antifungal phenols or the deactivation of phytoalexins.

In mushrooms

Significantly abundant in this group of organisms, laccases participate in a variety of cellular and physiological processes. Among them we can mention the protection of the pathogenic fungi of the tannins and the vegetal “phytoalexins”; so it can be said that, for fungi, these enzymes are virulence factors.

Laccases also have functions in the morphogenesis and differentiation of the resistance and spore structures of basidiomycetes, as well as in the biodegradation of lignin in fungi that degrade tissues of woody plant species.

At the same time, laccases participate in the formation of pigments in the mycelia and fruiting bodies of many fungi and contribute to the cell-cell adhesion processes, in the formation of the polyphenolic “glue” that binds the hyphae, and in evasion. of the immune system of hosts infected with pathogenic fungi.

In the industry

These particular enzymes are used industrially for various purposes, but the most outstanding ones correspond to the textile and paper industries and to the bioremediation and decontamination of wastewater produced by other industrial processes.

Specifically, these enzymes are frequently used for the oxidation of phenols and their derivatives present in water contaminated with industrial waste, whose catalysis products are insoluble (polymerized) and precipitate, which makes them easily separable.

In the food industry they are also of some importance since the removal of phenolic compounds is necessary for the stabilization of beverages such as wine, beer and natural juices.

They are used in the cosmetics industry, in the chemical synthesis of many compounds, in soil bioremediation and in nanobiotechnology.

The most widely used are laccase from fungi, but recently it has been determined that bacterial laccase has more prominent characteristics from an industrial point of view; They are capable of working with a greater variety of substrates and at much wider temperature and pH ranges, as well as being much more stable against inhibitory agents.

References

1. Claus, H. (2004). Laccases: structure, reactions, distribution. Micron, 35, 93–96.
2. Couto, SR, Luis, J., & Herrera, T. (2006). Industrial and biotechnological applications of laccases: A review. Biotechnology Advances, 24, 500–513.
3. Madhavi, V., & Lele, SS (2009). Laccase: properties and applications. Bioresources, 4 (4), 1694–1717.
4. Riva, S., Molecolare, R., & Bianco, VM (2006). Laccases: blue enzymes for green chemistry. Trends in Biotechnology, 24 (5), 219–226.
5. Singh, P., Bindi, C., & Arunika, G. (2017). Bacterial laccase: recent update on production, properties and industrial applications. Biotech, 7 (323), 1–20.