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Difference between revisions of "Glycoside Hydrolase Family 45"
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== Substrate specificities == | == Substrate specificities == | ||
− | [[Glycoside hydrolases]] of GH45 are endoglucanases (EC 3.2.1.4); mainly the hydrolysis of soluble beta 1,4 glucans. | + | [[Glycoside hydrolases]] of GH45 are endoglucanases (EC 3.2.1.4); mainly the hydrolysis of soluble β -1,4 glucans. |
== Kinetics and Mechanism == | == Kinetics and Mechanism == | ||
− | The enzymes, formally known as cellulase family "K" in some historic literature, act with inversion of anomeric configuration to generate the &alpha-D anomer of the oligosaccaride as product. Based upon the structure of the ''Humicola insolens'' endoglucanase V (now known as Cel45)<cite>Davies1993</cite><cite>Davies1995</cite> it was concluded that Asp121 acted as the [[general acid]] (implied by its hydrogen bonding to the glycosidic oxygen of a ligand in the +1 subsite) and that the most likely [[general base]] is Asp10, appropriately positioned "below" the sugar plane. As with many inverting enzymes the base assignment is less secure than that of the acid. | + | The enzymes, formally known as cellulase family "K" in some historic literature, act with inversion of anomeric configuration to generate the α-D anomer of the oligosaccaride as product. Based upon the structure of the ''Humicola insolens'' endoglucanase V (now known as Cel45)<cite>Davies1993</cite><cite>Davies1995</cite> it was concluded that Asp121 acted as the [[general acid]] (implied by its hydrogen bonding to the glycosidic oxygen of a ligand in the +1 subsite) and that the most likely [[general base]] is Asp10, appropriately positioned "below" the sugar plane. As with many inverting enzymes the base assignment is less secure than that of the acid. |
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== Three-dimensional structures == | == Three-dimensional structures == | ||
− | The 3-D structure of canonical GH45 enzymes is a six-stranded &beta-barrel to which a seventh strand is appended. The structure differs from classical &beta-barrels in containing both paralle and anti-parallel &beta-strands. At the time of the first structure solution the fold had ony previously been observed in "Barwin"; a plant defense protein of unknown function. As is now expected for ''endo''-enzymes, the active centre is located in an open substrate-binding groove. The original uncomplexes native structure had an disordered loop above the active centre and this was only seen to become ordered subsequently upon the binding of cello-oligosaccharides <cite>Davies1995</cite>. | + | The 3-D structure of canonical GH45 enzymes is a six-stranded &beta-barrel to which a seventh strand is appended. The structure differs from classical β-barrels in containing both paralle and anti-parallel β-strands. At the time of the first structure solution the fold had ony previously been observed in "Barwin"; a plant defense protein of unknown function. As is now expected for ''endo''-enzymes, the active centre is located in an open substrate-binding groove. The original uncomplexes native structure had an disordered loop above the active centre and this was only seen to become ordered subsequently upon the binding of cello-oligosaccharides <cite>Davies1995</cite>. |
− | Family GH45 enzymes are structurally related to plant <cite>Yennawar</cite> and bacterial <cite>Kerff</cite> expansins. Indeed they even display some of the catalytic centre motifs such as the catalytic acid | + | Family GH45 enzymes are structurally related to plant <cite>Yennawar</cite> and bacterial <cite>Kerff</cite> expansins. Indeed they even display some of the catalytic centre motifs such as the catalytic acid. |
Revision as of 07:08, 5 October 2010
This page is currently under construction. This means that the Responsible Curator has deemed that the page's content is not quite up to CAZypedia's standards for full public consumption. All information should be considered to be under revision and may be subject to major changes.
- Author: ^^^Gideon Davies^^^
- Responsible Curator: ^^^Gideon Davies^^^
Glycoside Hydrolase Family GH45 | |
Clan | none |
Mechanism | inverting |
Active site residues | known (but see discussion) |
CAZy DB link | |
http://www.cazy.org/fam/GH45.html |
Substrate specificities
Glycoside hydrolases of GH45 are endoglucanases (EC 3.2.1.4); mainly the hydrolysis of soluble β -1,4 glucans.
Kinetics and Mechanism
The enzymes, formally known as cellulase family "K" in some historic literature, act with inversion of anomeric configuration to generate the α-D anomer of the oligosaccaride as product. Based upon the structure of the Humicola insolens endoglucanase V (now known as Cel45)[1][2] it was concluded that Asp121 acted as the general acid (implied by its hydrogen bonding to the glycosidic oxygen of a ligand in the +1 subsite) and that the most likely general base is Asp10, appropriately positioned "below" the sugar plane. As with many inverting enzymes the base assignment is less secure than that of the acid.
Catalytic Residues
"Classical" GH45 enzymes likely use twin carboxylates corresponding to Asp10 and 121 of the Humicola insolens endoglucanase V [1][2].
Three-dimensional structures
The 3-D structure of canonical GH45 enzymes is a six-stranded &beta-barrel to which a seventh strand is appended. The structure differs from classical β-barrels in containing both paralle and anti-parallel β-strands. At the time of the first structure solution the fold had ony previously been observed in "Barwin"; a plant defense protein of unknown function. As is now expected for endo-enzymes, the active centre is located in an open substrate-binding groove. The original uncomplexes native structure had an disordered loop above the active centre and this was only seen to become ordered subsequently upon the binding of cello-oligosaccharides [2].
Family GH45 enzymes are structurally related to plant [3] and bacterial [4] expansins. Indeed they even display some of the catalytic centre motifs such as the catalytic acid.
Family Firsts
- First sterochemistry determination
- As part of an analysis of many families reported in [5].
- First general acid/base residue identification
- Catalytic residue proposals have been made solely on the basis of 3-D structure [1][2].
- First 3-D structure
- The Humicola insolens EGV (now Cel45) by the Davies group [1].
References
- Davies GJ, Dodson GG, Hubbard RE, Tolley SP, Dauter Z, Wilson KS, Hjort C, Mikkelsen JM, Rasmussen G, and Schülein M. (1993). Structure and function of endoglucanase V. Nature. 1993;365(6444):362-4. DOI:10.1038/365362a0 |
- Davies GJ, Tolley SP, Henrissat B, Hjort C, and Schülein M. (1995). Structures of oligosaccharide-bound forms of the endoglucanase V from Humicola insolens at 1.9 A resolution. Biochemistry. 1995;34(49):16210-20. DOI:10.1021/bi00049a037 |
- Yennawar NH, Li LC, Dudzinski DM, Tabuchi A, and Cosgrove DJ. (2006). Crystal structure and activities of EXPB1 (Zea m 1), a beta-expansin and group-1 pollen allergen from maize. Proc Natl Acad Sci U S A. 2006;103(40):14664-71. DOI:10.1073/pnas.0605979103 |
- Kerff F, Amoroso A, Herman R, Sauvage E, Petrella S, Filée P, Charlier P, Joris B, Tabuchi A, Nikolaidis N, and Cosgrove DJ. (2008). Crystal structure and activity of Bacillus subtilis YoaJ (EXLX1), a bacterial expansin that promotes root colonization. Proc Natl Acad Sci U S A. 2008;105(44):16876-81. DOI:10.1073/pnas.0809382105 |
- Schou C, Rasmussen G, Kaltoft MB, Henrissat B, and Schülein M. (1993). Stereochemistry, specificity and kinetics of the hydrolysis of reduced cellodextrins by nine cellulases. Eur J Biochem. 1993;217(3):947-53. DOI:10.1111/j.1432-1033.1993.tb18325.x |