Bacterial tyrosinases

Abstract

Tyrosinases are nearly ubiquitously distributed in all domains of life. They are essential for pigmentation and are important factors in wound healing and primary immune response. Their active site is characterized by a pair of antiferromagnetically coupled copper ions, CuA and CuB, which are coordinated by six histidine residues. Such a "type 3 copper centre" is the common feature of tyrosinases, catecholoxidases and haemocycanins. It is also one of several other copper types found in the multi-copper oxidases (ascorbate oxidase, laccase). The copper pair of tyrosinases binds one molecule of atmospheric oxygen to catalyse two different kinds of enzymatic reactions: (1) the ortho-hydroxylation of monophenols (cresolase activity) and (2) the oxidation of o-diphenols to o-diquinones (catecholase activity). The best-known function is the formation of melanins from L-tyrosine via L-dihydroxyphenylalanine (L-dopa). The complicated hydroxylation mechanism at the active centre is still not completely understood, because nothing is known about their tertiary structure. One main reason for this deficit is that hitherto tyrosinases from eukaryotic sources could not be isolated in sufficient quantities and purities for detailed structural studies. This is not the case for prokaryotic tyrosinases from different Streptomyces species, having been intensively characterized genetically and spectroscopically for decades. The Streptomyces tyrosinases are non-modified monomeric proteins with a low molecular mass of ca. 30kDa. They are secreted to the surrounding medium, where they are involved in extracellular melanin production. In the species Streptomyces, the tyrosinase gene is part of the melC operon. Next to the tyrosinase gene (melC2), this operon contains an additional ORF called melC1, which is essential for the correct expression of the enzyme. This review summarizes the present knowledge of bacterial tyrosinases, which are promising models in order to get more insights in structure, enzymatic reactions and functions of "type 3 copper" proteins in general.

Melanins: Skin Pigments and Much More—Types, Structural Models, Biological Functions, and Formation Routes

“…In this regard, bacterial laccases (EC 1.10.3.2) are still widespread in bacteria and economically attractive because purification of enzymes from bacteria is relatively simple and inexpensive, although tyrosinases occur more frequently than laccases in the bacterial kingdom [247]. Different bacterial tyrosinases [248,249] have also been proposed for "in vitro" melanin preparation.…”

Enzymes for Wine Fermentation: Current and Perspective Applications

“…Spontaneous and enzymatic oxidations exert dramatic effects on the final phenolic composition from the grape berry to bottled wine [82,83]. Once the integrity of the berries is destroyed, oxidative enzymes (phenoloxidases) and their phenolic substrates are exposed to the air, resulting in enzymatic browning (Figure 2).…”

“…Once the integrity of the berries is destroyed, oxidative enzymes (phenoloxidases) and their phenolic substrates are exposed to the air, resulting in enzymatic browning (Figure 2). There are two classes of copper enzymes responsible for these reactions [82,83]: Tyrosinase (E.C. 1.14.18.1) hydroxylates monophenols to ortho-diphenols and oxidizes the latter to ortho-quinone intermediates which easily react further to polymeric, mostly colored products.…”

“…These enzymes belong to the class of type 2 or "non-blue" copper proteins which convert primary amines to the corresponding aldehydes with an equimolar consumption of molecular oxygen and formation of hydrogen peroxide and ammonia. There are two classes of copper enzymes responsible for these reactions [82,83]: Tyrosinase (E.C. 1.14.18.1) hydroxylates monophenols to ortho-diphenols and oxidizes the latter to ortho-quinone intermediates which easily react further to polymeric, mostly colored products.…”

Investigation of gene family evolution and the molecular basis of shell formation in molluscs

“…Copper-binding proteins are present in the three domains of life (van Holde and Miller 1995, van Gelder et al 1997, Claus and Decker 2006, Andreini et al 2008 and are divided into three classes based on their spectroscopic properties and geometric structure of the active site: type-1 or blue copper proteins, which are involved in electron-transfer (e.g. plastocyanin, azurin and halocyanin); type-2 or non-blue copper proteins, which form part of the oxidoreductase family (e.g.…”