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| − | <!-- RESPONSIBLE CURATORS: Please replace the {{UnderConstruction}} tag below with {{CuratorApproved}} when the page is ready for wider public consumption -->
| + | * [[Responsible Curator]]: ^^^Bernard Henrissat^^^ |
| | + | ---- |
| | + | |
| | {{CuratorApproved}} | | {{CuratorApproved}} |
| − | * [[Author]]: ^^^Alan Cartmell^^^
| + | {{DeletedFamily}} |
| − | * [[Responsible Curator]]: ^^^Alan Cartmell^^^
| + | |
| − | ----
| + | === GH145 is a deleted family === |
| | + | |
| | + | This family has been reclassified as [[Polysaccharide Lyase Family 42]]. Further information can be found on the [[PL42]] page and the header of the [{{CAZyDBlink}}GH145.html GH145 page in the CAZy database]. |
| | | | |
| | + | '''References''' |
| | + | <biblio> |
| | + | </biblio> |
| | <!-- The data in the table below should be updated by the Author/Curator according to current information on the family --> | | <!-- The data in the table below should be updated by the Author/Curator according to current information on the family --> |
| − | <div style="float:right">
| + | {| {{Prettytable}} |
| − | | |
| − | {| {{Prettytable}} | |
| − | |-
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| − | | {{Hl2}} colspan="2" align="center" |'''Glycoside Hydrolase Family GH145'''
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| − | |-
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| − | | '''Clan'''
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| − | | None
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| | |- | | |- |
| − | | '''Mechanism'''
| + | |{{Hl2}} colspan="2" align="center" |'''CAZy DB links''' |
| − | | retaining
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| − | |-
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| − | | '''Active site residues'''
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| − | | known
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| − | |-
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| − | | {{Hl2}} colspan="2" align="center" |'''CAZy DB link''' | |
| | |- | | |- |
| | | colspan="2" |{{CAZyDBlink}}GH145.html | | | colspan="2" |{{CAZyDBlink}}GH145.html |
| − | |}
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| | | | |
| − | </div>
| + | |- |
| | + | | colspan="2" |{{CAZyDBlink}}PL42.html |
| | | | |
| | + | |} |
| | <!-- This is the end of the table --> | | <!-- This is the end of the table --> |
| − | == Substrate specificities ==
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| − | Two members of this family have been shown to be an exo-α-L-rhamnosidases, targeting rhamnose linked α-1,4 to glucuronic acid in the complex arabinogalactan protein gum arabic <cite>Munoz-Munoz2017 Cartmell2019</cite>.
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| − |
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| − | == Kinetics and Mechanism ==
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| − | NMR, using the arabinogalactan protein (AGP) gum arabic as the substrate, revealed the family operates via a retaining mechanism <cite>Munoz-Munoz2017</cite>. Rather than using a standard double displacement mechanism the enzyme is speculatively predicted to perform catalysis via an epoxide intermediate, similar to GH99 enzymes <cite>Thompson2012 Fernandes2018</cite>. GH145, however, is proposed to perform catalysis via a substrate assisted mechanism, requiring the carboxyl group of the glucuronic acid and a single catalytic histidine; both acting as an acid/base. This histidine is predicted to deprotonate the O2 of rhamnose, allowing O2 to attack C1 and form an epoxide. Simultaneously the carboxyl group of the glucuronic acid may deprotonate a water molecule generating a hydroxyl group to attach the C1 of rhamnose and allowing protonation of its own O4 thus, leading to glycosidic bond cleavage <cite>Munoz-Munoz2017</cite>. Further work is needed to confirm the mechanism by which GH145 operates.
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| − |
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| − | == Catalytic Residues ==
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| − | A single catalytic histidine, His48 in BT3686, has been shown to be critical for activity. This was the only residue mutated (to Gln, Ala and Gly) that caused loss of activity and is thought to act as an acid/base. Several homologues of BT3686 exist, which although >80 % identical are inactive due to having Gln at the equivalent position to His48 in BT3686. The introduction of a histidine at into related enzymes BACINT_00347 and BACCELL_00856, from ''Bacteroides intestinalis'' and ''Bacteroides cellulosilyticus'', generating the mutants Q48H in both proteins, is sufficient to introduce rhamnosidase activity into these, otherwise inactive, enzymes <cite>Munoz-Munoz2017</cite>. No second catalytic residue to could be identified and it was tentatively proposed that the glucurnonic acid participates as a second acid/base residue, portonating its own O4 and activating a water molecule.
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| − |
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| − | == Three-dimensional structures ==
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| − | GH145 comprise a single domain which is a seven bladed β-propeller fold. Each blade is composed of four anti parallel β-strands that extend out radially from the central core. The final blade is formed by strands from both the N- and C-terminus of the protein which is termed as 'molecular velcro' and is believed to add considerable stability to the fold. The active site of these α-L-rhamnosidases is located on the opposite side, termed the posterior surface, of CAZymes with similar β-propeller folds. The "normal" side, termed the anterior surface, of the β-propeller bears the highest residue conservation and may well have another function. GH145 is distantly related to [[PL25]] which utilise the anterior surface suggesting that the this surface in GH145 may have another activity <cite>Munoz-Munoz2017 Ulaganathan2017</cite>.
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| − |
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| − | == Family Firsts ==
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| − | ;First stereochemistry determination: Determined for the ''bacteroides thetaiotaomicron'' enzyme BT3686 <cite>Munoz-Munoz2017</cite>.
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| − | ;First catalytic acid/base residue identification: Predicted to be a histidine <cite>Munoz-Munoz2017</cite>.
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| − | ;Second general acid/base residue identification: Predicted to be provided by the substrate <cite>Munoz-Munoz2017</cite>.
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| − | ;First 3-D structure: BT3686, BACINT_00347 and BACCELL_00856 were the first enzymes to have their structures solved from the organisms ''bacteroides thetaiotaomicron'', ''bacteroides intestinalis'' and ''bacteroides cellulosilyticus'', respectively. <cite>Munoz-Munoz2017</cite>.
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| − |
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| − | == References ==
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| − | <biblio>
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| − | #Munoz-Munoz2017 pmid=28396425
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| − | #Cartmell2019 pmid=31541200
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| − | #Thompson2012 pmid=22219371
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| − | #Fernandes2018 pmid=29508463
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| − | #Ulaganathan2017 pmid=28290654
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| − | </biblio>
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| − |
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| | | | |
| | [[Category:Glycoside Hydrolase Families|GH145]] | | [[Category:Glycoside Hydrolase Families|GH145]] |
