| Description | Copper is one of the most prevalent transition metals in living organisms and its biological function is intimately related to its redox properties. Since free copper is toxic, even at very low concentrations, its homeostasis in living organisms is tightly controlled by subtle molecular mechanisms. In eukaryotes, before being transported inside the cell via the high-affinity copper transporters of the CTR family, the copper (II) ion is reduced to copper (I). In blue copper proteins such as cupredoxin, the copper (I) ion form is stabilised by a constrained His2Cys coordination environment.Multicopper oxidases oxidise their substrate by accepting electrons at a mononuclear copper centre and transferring them to a trinuclear copper centre; dioxygen binds to the trinuclear centre and, following the transfer of four electrons, is reduced to two molecules of water [ ]. There are three spectroscopically different copper centres found in multicopper oxidases: type 1 (or blue), type 2 (or normal) and type 3 (or coupled binuclear) [, ]. Multicopper oxidases consist of 2, 3 or 6 of these homologous domains, which also share homology to the cupredoxins azurin and plastocyanin. Structurally, these domains consist of a cupredoxin-like fold, a β-sandwich consisting of 7 strands in 2 β-sheets, arranged in a Greek-key β-barrel []. Multicopper oxidases include:Laccase ( ) (urishiol oxidase), a 3-domain enzyme found in fungi and plants, which oxidises different phenols and diamines. CueO is a laccase found in Escherichia coli that is involved in copper-resistance [ ].Ascorbate oxidase ( ), a 3-domain enzyme found in higher plants. Nitrite reductase ( ), a 2-domain enzyme containing type-1 and type-2 copper centres [ , ].Fission yeast fio1 (also known as SpAC1F7.08), a multicopper oxidase that contains three cupredoxin domains and may function together with Frp1 in iron and copper uptakes in S. pombe [ ].In addition to the above enzymes there are a number of other proteins that are similar to the multi-copper oxidases in terms of structure and sequence, some of which have lost the ability to bind copper. These include: copper resistance protein A (copA) from a plasmid in Pseudomonas syringae; domain A of (non-copper binding) blood coagulation factors V (Fa V) and VIII (Fa VIII) [ ]; yeast FET3 required for ferrous iron uptake [] and yeast FET5 (YFL041w), which similarly to FET3 it is an iron transport multicopper oxidase required for Fe2 ion high affinity uptake []. It is targeted to vacuole via AP-3 pathway []. Ferroxidase HEPHL1, included in this entry, is a copper-binding glycoprotein with ferroxidase activity that oxidises Fe2 to Fe3 without releasing radical oxygen species []. It may be involved in the regulation of intracellular iron content[]. | Name | Multicopper oxidase |
| Short Name | Cu-oxidase_fam | Type | Family |
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