Sandbox Reserved 1104: Difference between revisions

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Multicopper oxidases are enzymes which oxidise their substrate by accepting electrons at a mononuclear copper centre and transferring them to a trinuclear copper centre.<ref>Wikipedia, Multicopper oxidase [https://en.wikipedia.org/wiki/Multicopper_oxidase]</ref>

Bilirubin oxidases are multicopper oxidases containing type 1, type 2, and type 3 coppers. Indeed, there is strong sequence homology between bilirubin oxidase and multicopper oxidases like [[laccase]], ascorbate oxidase and even [[ceruloplasmin]]. Moreover, the His-Cys-His sequence, characteristic of multicopper oxidase, is present in bilirubin oxidase. Copper is essential for the enzyme activity.<ref name="multic">DOI 10.1021/bi9819531</ref>

Bilirubin oxidases are multicopper oxidases containing type 1, type 2, and type 3 coppers. Indeed, there is strong sequence homology between bilirubin oxidase and multicopper oxidases like [[laccase]], ascorbate oxidase and even [[ceruloplasmin]]. Moreover, the <scene name='82/829357/His-cys-his/1'>His-Cys-His</scene> sequence, characteristic of multicopper oxidase, is present in bilirubin oxidase. Copper is essential for the enzyme activity.<ref name="multic">DOI 10.1021/bi9819531</ref>

Copper is classified into three types according to their optical and magnetic properties. Type 1 copper (or blue copper) shows many charge-transfer bands around 450 nm, 600 nm and 750 nm. The most peculiar band appears around 600 nm and represents the Cys to Cu(II) charge transfer. Type 2 copper (or nonblue copper) does not show any strong charge-transfer bands in the visible region. Type 3 coppers are not detectable by ESR because some are antiferromagnetically coupled. However, a hydroxide ion links them and so gives a strong absorption at 330 nm.<ref name="multic"/>

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Among the multicopper oxidases, bilirubin oxidase is the only one which forms this <scene name='82/829357/Trp-his_covalent_bond/1'>His-Trp link</scene>. It is due to the particular molecular environment of the <scene name='82/829357/Trp396/1'>Trp396</scene> residue, which is unique among the multicopper oxidases registered in the PDB. Indeed, the equivalent position is occupied by a glutamate side chain in multicopper oxidases from ''Thermus thermophilus'' ([[2xu9]]) and ''Campylobacter jejuni'' ([[3zx1]]), by aspartate in yeast Fet3p ([[1zpu]]), and by a main chain carbonyl oxygen atom in laccases from ''Antrodiella faginea'' ([[5ehf]]), ''Cerrena maxima'' ([[5h5u]]), ''Coriolus zonatus'' ([[2hzh]]), ''Lentinus sp.'' ([[3x1b]]), ''Lentinus tigrinus'' ([[2qt6]]), ''Steccherinum murashkinskyi'' ([[5mig]]), ''Trametes hirsuta'' ([[3fpx]]), and ''Trametes sp.'' AH28-2 ([[3kw7]]) <ref name="stru"/>.

The role of this covalent bond between the indole ring of <scene name='82/829357/Trp396/1'>Trp396</scene> and the imidazole ring of <scene name='82/829357/His398/1'>His398</scene> has been investigated using mutants of bilirubin oxidase (at the position 396). Their enzymatic activities have been compared with the one of wild type bilirubin oxidase. All the mutations have led to a significant decrease of the catalytic efficiency for bilirubin, compared to the wild type bilirubin oxidase. It proves that the <scene name='82/829357/Trp-his_covalent_bond/1'>Trp396-His398</scene> ~~covalent bond~~ has a major role in the enzymatic activity of bilirubin oxidase. However, it has no influence on the enzyme structure (except the replaced residue), since bilirubin can still bind to mutants not containing tryptophan at the position 396. Moreover, bilirubin is oxidized even in the absence of the Trp-His covalent bond, proving that its role in electron transfer is not crucial <ref name="struct"/>.

The role of this covalent bond between the indole ring of <scene name='82/829357/Trp396/1'>Trp396</scene> and the imidazole ring of <scene name='82/829357/His398/1'>His398</scene> has been investigated using mutants of bilirubin oxidase (at the position 396). Their enzymatic activities have been compared with the one of wild type bilirubin oxidase. All the mutations have led to a significant decrease of the catalytic efficiency for bilirubin, compared to the wild type bilirubin oxidase. It proves that the <scene name='82/829357/Trp-his_covalent_bond/1'>Trp396-His398 covalent bond</scene> has a major role in the enzymatic activity of bilirubin oxidase. However, it has no influence on the enzyme structure (except the replaced residue), since bilirubin can still bind to mutants not containing tryptophan at the position 396. Moreover, bilirubin is oxidized even in the absence of the <scene name='82/829357/Trp-his_covalent_bond/1'>Trp-His covalent bond</scene>, proving that its role in electron transfer is not crucial <ref name="struct"/>.

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@@ Line 15: / Line 15: @@
 Multicopper oxidases are enzymes which oxidise their substrate by accepting electrons at a mononuclear copper centre and transferring them to a trinuclear copper centre.<ref>Wikipedia, Multicopper oxidase [https://en.wikipedia.org/wiki/Multicopper_oxidase]</ref>
-Bilirubin oxidases are multicopper oxidases containing type 1, type 2, and type 3 coppers. Indeed, there is strong sequence homology between bilirubin oxidase and multicopper oxidases like [[laccase]], ascorbate oxidase and even [[ceruloplasmin]]. Moreover, the His-Cys-His sequence, characteristic of multicopper oxidase, is present in bilirubin oxidase. Copper is essential for the enzyme activity.<ref name="multic">DOI 10.1021/bi9819531</ref>
+Bilirubin oxidases are multicopper oxidases containing type 1, type 2, and type 3 coppers. Indeed, there is strong sequence homology between bilirubin oxidase and multicopper oxidases like [[laccase]], ascorbate oxidase and even [[ceruloplasmin]]. Moreover, the <scene name='82/829357/His-cys-his/1'>His-Cys-His</scene> sequence, characteristic of multicopper oxidase, is present in bilirubin oxidase. Copper is essential for the enzyme activity.<ref name="multic">DOI 10.1021/bi9819531</ref>
 Copper is classified into three types according to their optical and magnetic properties. Type 1 copper (or blue copper) shows many charge-transfer bands around 450 nm, 600 nm and 750 nm. The most peculiar band appears around 600 nm and represents the Cys to Cu(II) charge transfer. Type 2 copper (or nonblue copper) does not show any strong charge-transfer bands in the visible region. Type 3 coppers are not detectable by ESR because some are antiferromagnetically coupled. However, a hydroxide ion links them and so gives a strong absorption at 330 nm.<ref name="multic"/>
@@ Line 28: / Line 28: @@
 Among the multicopper oxidases, bilirubin oxidase is the only one which forms this <scene name='82/829357/Trp-his_covalent_bond/1'>His-Trp link</scene>. It is due to the particular molecular environment of the <scene name='82/829357/Trp396/1'>Trp396</scene> residue, which is unique among the multicopper oxidases registered in the PDB. Indeed, the equivalent position is occupied by a glutamate side chain in multicopper oxidases from ''Thermus thermophilus'' ([[2xu9]]) and ''Campylobacter jejuni'' ([[3zx1]]), by aspartate in yeast Fet3p ([[1zpu]]), and by a main chain carbonyl oxygen atom in laccases from ''Antrodiella faginea'' ([[5ehf]]), ''Cerrena maxima'' ([[5h5u]]), ''Coriolus zonatus'' ([[2hzh]]), ''Lentinus sp.'' ([[3x1b]]), ''Lentinus tigrinus'' ([[2qt6]]), ''Steccherinum murashkinskyi'' ([[5mig]]), ''Trametes hirsuta'' ([[3fpx]]), and ''Trametes sp.'' AH28-2 ([[3kw7]]) <ref name="stru"/>.
-The role of this covalent bond between the indole ring of <scene name='82/829357/Trp396/1'>Trp396</scene> and the imidazole ring of <scene name='82/829357/His398/1'>His398</scene> has been investigated using mutants of bilirubin oxidase (at the position 396). Their enzymatic activities have been compared with the one of wild type bilirubin oxidase. All the mutations have led to a significant decrease of the catalytic efficiency for bilirubin, compared to the wild type bilirubin oxidase. It proves that the <scene name='82/829357/Trp-his_covalent_bond/1'>Trp396-His398</scene> covalent bond has a major role in the enzymatic activity of bilirubin oxidase. However, it has no influence on the enzyme structure (except the replaced residue), since bilirubin can still bind to mutants not containing tryptophan at the position 396. Moreover, bilirubin is oxidized even in the absence of the Trp-His covalent bond, proving that its role in electron transfer is not crucial <ref name="struct"/>.
+The role of this covalent bond between the indole ring of <scene name='82/829357/Trp396/1'>Trp396</scene> and the imidazole ring of <scene name='82/829357/His398/1'>His398</scene> has been investigated using mutants of bilirubin oxidase (at the position 396). Their enzymatic activities have been compared with the one of wild type bilirubin oxidase. All the mutations have led to a significant decrease of the catalytic efficiency for bilirubin, compared to the wild type bilirubin oxidase. It proves that the <scene name='82/829357/Trp-his_covalent_bond/1'>Trp396-His398 covalent bond</scene> has a major role in the enzymatic activity of bilirubin oxidase. However, it has no influence on the enzyme structure (except the replaced residue), since bilirubin can still bind to mutants not containing tryptophan at the position 396. Moreover, bilirubin is oxidized even in the absence of the <scene name='82/829357/Trp-his_covalent_bond/1'>Trp-His covalent bond</scene>, proving that its role in electron transfer is not crucial <ref name="struct"/>.
 == Function ==