Glycoside Hydrolase Family 17 - Revision history

Harry Brumer: Text replacement - "\^\^\^(.*)\^\^\^" to "$1"

2021-12-18T21:20:16Z

Text replacement - "\^\^\^(.*)\^\^\^" to "$1"

Harry Brumer: /* Substrate specificities */

2012-10-18T14:11:07Z

Substrate specificities

Harry Brumer: updated CAZyDBlink

2012-09-10T16:32:59Z

updated CAZyDBlink

Harry Brumer: /* Three-dimensional structures */

2010-07-01T12:03:03Z

Three-dimensional structures

Spencer Williams at 11:54, 14 June 2010

2010-06-14T11:54:29Z

Spencer Williams at 11:45, 9 June 2010

2010-06-09T11:45:22Z

Bernard Henrissat at 15:06, 27 April 2010

2010-04-27T15:06:55Z

Bernard Henrissat at 15:06, 27 April 2010

2010-04-27T15:06:33Z

Bernard Henrissat: /* Family Firsts */

2010-04-27T15:05:24Z

Family Firsts

Bernard Henrissat: /* Three-dimensional structures */

2010-04-27T15:03:53Z

Three-dimensional structures

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 <!-- CURATORS: Please replace the {{UnderConstruction}} tag below with {{CuratorApproved}} when the page is ready for wider public consumption -->
 {{CuratorApproved}}
-* [[Author]]: ^^^Geoff Fincher^^^
+* [[Author]]: [[User:Geoff Fincher|Geoff Fincher]]
-* [[Responsible Curator]]:  ^^^Bernard Henrissat^^^
+* [[Responsible Curator]]:  [[User:Bernard Henrissat|Bernard Henrissat]]
 ----

@@ Line 29: / Line 29: @@
 == Substrate specificities ==
-The family GH17 [[glycoside hydrolase]]s are [[Sequence-based classification of glycoside hydrolases|clan]] GH-A enzymes from bacteria, fungi and plants, and include two major groups of enzymes with related but distinct substrate specificities, namely 1,3-β-D-glucan [[endo]]hydrolases ([{{EClink}}3.2.1.39 EC 3.2.1.39]) and 1,3;1,4-β-D-glucan endohydrolases ([{{EClink}}3.2.1.73 EC 3.1.2.73]).  A 1,3-β-D-glucan exohydrolase ([{{EClink}}3.2.1.58 EC 3.1.2.58]) is also classified in this family.  The family GH17 enzymes have quite distinct amino acid sequences and 3D structures compared with the 1,3-β-D-glucan endohydrolases and 1,3;1,4-β-D-glucan [[endo]]hydrolases that have similar substrate specificities but are classified in families [[GH16]], [[GH55]], GH64 and GH81.
+The family GH17 [[glycoside hydrolase]]s are [[Sequence-based classification of glycoside hydrolases|clan]] GH-A enzymes from bacteria, fungi and plants, and include two major groups of enzymes with related but distinct substrate specificities, namely 1,3-β-D-glucan [[endo]]hydrolases ([{{EClink}}3.2.1.39 EC 3.2.1.39]) and 1,3;1,4-β-D-glucan endohydrolases ([{{EClink}}3.2.1.73 EC 3.1.2.73]).  A 1,3-β-D-glucan exohydrolase ([{{EClink}}3.2.1.58 EC 3.1.2.58]) is also classified in this family.  The family GH17 enzymes have quite distinct amino acid sequences and 3D structures compared with the 1,3-β-D-glucan endohydrolases and 1,3;1,4-β-D-glucan [[endo]]hydrolases that have similar substrate specificities but are classified in families [[GH16]], [[GH55]], [[GH64]] and [[GH81]].
 The family GH17 1,3-β-D-glucan [[endo]]hydrolases hydrolyse internal 1,3-β-D-glucosidic linkages in polysaccharides, but usually require a region of contiguous unbranched, un-substituted 1,3-β-D-glucosyl residues for activity.  The enzymes release 1,3-β-D-oligoglucosides of DP 2-5 as their major products. Because the 1,3-β-D-glucan endohydrolases require a region of contiguous unbranched, unsubstituted 1,3-β-D-glucosyl residues for activity, they are unable to hydrolyse the single 1,3-β-D-glucosidic linkages in 1,3;1,4-β-D-glucans from the Poaceae, but they will hydrolyse  1,3-β-D-glucosidic linkages in fungal 1,3;1,6-β-D-glucans, provided an appropriate region of contiguous un-substituted 1,3-β-D-glucosyl residues is available. The family GH17 1,3;1,4-β-D-glucan endohydrolases ([{{EClink}}3.2.1.73 EC 3.1.2.73]) hydrolyse 1,4-β-D-glucosidic linkages, but only 1,3;1,4-β-D-glucans in which the glucosyl residue involved in the glycosidic linkage cleaved is substituted at the C(0)3 position, that is, where the 1,4-β-D-glucosidic linkages are located on the reducing end side of 1,3-β-D-glucosyl residues.

@@ Line 22: / Line 22: @@
 |{{Hl2}} colspan="2" align="center" |'''CAZy DB link'''
 |-
-| colspan="2" |http://www.cazy.org/fam/GH17.html
+| colspan="2" |{{CAZyDBlink}}GH17.html
 |}
 </div>

@@ Line 42: / Line 42: @@
 == Three-dimensional structures ==
-[[Image:GH17Superimposition.png|thumb|right|250px|'''Superposition of the polypeptide backbones of the barley (1,3)-β-D-glucan endohydrolase isoenzyme GII (green) and (1,3;1,4)-β-D-glucan endohydrolase isoenzyme EII (yellow). From <cite>Varghese</cite>''']]
+[[Image:GH17Superimposition.png|thumb|right|250px|Superposition of the polypeptide backbones of the barley (1,3)-β-D-glucan endohydrolase isoenzyme GII (green) and (1,3;1,4)-β-D-glucan endohydrolase isoenzyme EII (yellow). From <cite>Varghese</cite>]]
 The crystal structures of the barley 1,3-β-D-glucan endohydrolase isoenzyme GII and 1,3;1,4-β-D-glucan endohydrolase isoenzyme EII have been solved to 2.2-2.3 Å resolution and shown to adopt essentially identical (β/α)<sub>8</sub> TIM barrel structures <cite>Varghese</cite>.  The rms deviation in Cα positions between the two barley enzymes is 0.65 Å for 278 residues <cite>Varghese</cite>. This indicates that only minor differences in structure and amino acid dispositions at the substrate-binding and catalytic sites are sufficient to change a pre-existing 1,3-β-D-glucan endohydrolase into a highly specific 1,3;1,4-β-D-glucan endohydrolase <cite>Varghese</cite>.

@@ Line 29: / Line 29: @@
 == Substrate specificities ==
-The family GH17 [[glycoside hydrolase]]s are clan GH-A enzymes from bacteria, fungi and plants, and include two major groups of enzymes with related but distinct substrate specificities, namely 1,3-β-D-glucan [[endo]]hydrolases ([{{EClink}}3.2.1.39 EC 3.2.1.39]) and 1,3;1,4-β-D-glucan endohydrolases ([{{EClink}}3.2.1.73 EC 3.1.2.73]).  A 1,3-β-D-glucan exohydrolase ([{{EClink}}3.2.1.58 EC 3.1.2.58]) is also classified in this family.  The family GH17 enzymes have quite distinct amino acid sequences and 3D structures compared with the 1,3-β-D-glucan endohydrolases and 1,3;1,4-β-D-glucan [[endo]]hydrolases that have similar substrate specificities but are classified in families [[GH16]], [[GH55]], GH64 and GH81.
+The family GH17 [[glycoside hydrolase]]s are [[Sequence-based classification of glycoside hydrolases|clan]] GH-A enzymes from bacteria, fungi and plants, and include two major groups of enzymes with related but distinct substrate specificities, namely 1,3-β-D-glucan [[endo]]hydrolases ([{{EClink}}3.2.1.39 EC 3.2.1.39]) and 1,3;1,4-β-D-glucan endohydrolases ([{{EClink}}3.2.1.73 EC 3.1.2.73]).  A 1,3-β-D-glucan exohydrolase ([{{EClink}}3.2.1.58 EC 3.1.2.58]) is also classified in this family.  The family GH17 enzymes have quite distinct amino acid sequences and 3D structures compared with the 1,3-β-D-glucan endohydrolases and 1,3;1,4-β-D-glucan [[endo]]hydrolases that have similar substrate specificities but are classified in families [[GH16]], [[GH55]], GH64 and GH81.
-The family GH17 1,3-β-D-glucan [[endo]]hydrolases hydrolyse internal 1,3-β-D-glucosidic linkages in polysaccharides, but usually require a region of contiguous unbranched, un-substituted 1,3-β-D-glucosyl residues for activity.  The enzymes release 1,3-β-D-oligoglucosides of DP 2-5 as their major products. Because the 1,3-β-D-glucan endohydrolases require a region of contiguous unbranched, un-substituted 1,3-β-D-glucosyl residues for activity, they are unable to hydrolyse the single 1,3-β-D-glucosidic linkages in 1,3;1,4-β-D-glucans from the Poaceae, but they will hydrolyse  1,3-β-D-glucosidic linkages in fungal 1,3;1,6-β-D-glucans, provided an appropriate region of contiguous un-substituted 1,3-β-D-glucosyl residues is available. The family GH17 1,3;1,4-β-D-glucan endohydrolases ([{{EClink}}3.2.1.73 EC 3.1.2.73]) hydrolyse 1,4-β-D-glucosidic linkages, but only 1,3;1,4-β-D-glucans in which the glucosyl residue involved in the glycosidic linkage cleaved is substituted at the C(0)3 position, that is, where the 1,4-β-D-glucosidic linkages are located on the reducing end side of 1,3-β-D-glucosyl residues.
+The family GH17 1,3-β-D-glucan [[endo]]hydrolases hydrolyse internal 1,3-β-D-glucosidic linkages in polysaccharides, but usually require a region of contiguous unbranched, un-substituted 1,3-β-D-glucosyl residues for activity.  The enzymes release 1,3-β-D-oligoglucosides of DP 2-5 as their major products. Because the 1,3-β-D-glucan endohydrolases require a region of contiguous unbranched, unsubstituted 1,3-β-D-glucosyl residues for activity, they are unable to hydrolyse the single 1,3-β-D-glucosidic linkages in 1,3;1,4-β-D-glucans from the Poaceae, but they will hydrolyse  1,3-β-D-glucosidic linkages in fungal 1,3;1,6-β-D-glucans, provided an appropriate region of contiguous un-substituted 1,3-β-D-glucosyl residues is available. The family GH17 1,3;1,4-β-D-glucan endohydrolases ([{{EClink}}3.2.1.73 EC 3.1.2.73]) hydrolyse 1,4-β-D-glucosidic linkages, but only 1,3;1,4-β-D-glucans in which the glucosyl residue involved in the glycosidic linkage cleaved is substituted at the C(0)3 position, that is, where the 1,4-β-D-glucosidic linkages are located on the reducing end side of 1,3-β-D-glucosyl residues.
 Reaction products released are mainly 1,3;1,4-β-D-tri- and tetrasaccharides (G4G3G<sub>red</sub> and G4G4G3G<sub>red</sub>), but they also release higher oligosaccharides of up to 10 or more contiguous 1,4-β-D-glucosyl residues with a single reducing terminal 1,3-β-D-glucosyl residue (e.g. G4G4G4G4G4G4G3G<sub>red</sub>).  These longer oligosaccharides originate from the longer regions of adjacent 1,4-linkages that account for approximately 10% by weight of 1,3;1,4-β-D-glucans in cell walls of the [http://en.wikipedia.org/wiki/Poaceae Poaceae] <cite>Woodward</cite>.
@@ Line 39: / Line 39: @@
 == Catalytic Residues ==
-Active site labelling with epoxyalkyl-β-D-oligoglucoside inhibitors identified Glu231 and Glu232 as the [[catalytic nucleophile]]s of the barley 1,3- and 1,3;1,4-β-D-glucan endohydrolases, respectively <cite>Chen1993</cite>, located at the bottom of, and about two-thirds of the way along the substrate binding cleft.  The [[general acid/base]] residue of 1,3;1,4-β-D-glucan endohydrolase was initially identified as Glu288 by chemical labelling procedures <cite>Chen1993 Chen1995b</cite>, but this assignment was subsequently revised and Glu93 was proposed based on primary and tertiary structure similarity of GH17 enzymes with clan GH-A β-glycosidases <cite>Jenkins1998 Henrissat</cite>. The 5-6 Å distance between Glu232 and Glu93 is typical of retaining enzymes.
+Active site labelling with epoxyalkyl β-D-oligoglucoside inhibitors identified Glu231 and Glu232 as the [[catalytic nucleophile]]s of the barley 1,3- and 1,3;1,4-β-D-glucan endohydrolases, respectively <cite>Chen1993</cite>, located at the bottom of, and about two-thirds of the way along the substrate binding cleft.  The [[general acid/base]] residue of 1,3;1,4-β-D-glucan endohydrolase was initially identified as Glu288 by chemical labelling procedures <cite>Chen1993 Chen1995b</cite>, but this assignment was subsequently revised and Glu93 was proposed based on primary and tertiary structure similarity of GH17 enzymes with clan GH-A β-glycosidases <cite>Jenkins1998 Henrissat</cite>. The 5-6 Å distance between Glu232 and Glu93 is typical of [[retaining]] enzymes.
 == Three-dimensional structures ==
@@ Line 45: / Line 45: @@
 The crystal structures of the barley 1,3-β-D-glucan endohydrolase isoenzyme GII and 1,3;1,4-β-D-glucan endohydrolase isoenzyme EII have been solved to 2.2-2.3 Å resolution and shown to adopt essentially identical (β/α)<sub>8</sub> TIM barrel structures <cite>Varghese</cite>.  The rms deviation in Cα positions between the two barley enzymes is 0.65 Å for 278 residues <cite>Varghese</cite>. This indicates that only minor differences in structure and amino acid dispositions at the substrate-binding and catalytic sites are sufficient to change a pre-existing 1,3-β-D-glucan endohydrolase into a highly specific 1,3;1,4-β-D-glucan endohydrolase <cite>Varghese</cite>.
-A deep substrate-binding cleft extends across the surface of the enzyme and can accommodate 6-8 glucosyl-binding subsites <cite>Varghese</cite>.  The open cleft enables the enzyme to bind at essentially any position along the 1,3;1,4-β-D-glucan substrate and hence to hydrolyse internal glycoside linkages. Like in other clan GH-A structures, the catalytic acid/base and nucleophile glutamates are positioned on strands β-4 and β-7 <cite>Varghese Jenkins1998 Henrissat</cite>.
+A deep substrate-binding cleft extends across the surface of the enzyme and can accommodate 6-8 glucosyl-binding subsites <cite>Varghese</cite>.  The open cleft enables the enzyme to bind at essentially any position along the 1,3;1,4-β-D-glucan substrate and hence to hydrolyse internal glycoside linkages. Like in other [[Sequence-based classification of glycoside hydrolases|clan]] GH-A structures, the [[general acid/base]] and [[catalytic nucleophile]] glutamates are positioned on strands β-4 and β-7 <cite>Varghese Jenkins1998 Henrissat</cite>.
 The X-ray crystallographic data provide compelling evidence that the 1,3;1,4-β-D-glucan endohydrolases of barley evolved via the recruitment of pre-existing and widely distributed family GH17 1,3-β-D-glucan endohydrolases [6].  The similarities in substrate specificity between family GH17 and [[GH16]] enzymes has arisen through convergent evolution; the family [[GH16]] enzymes are members of clan-B and have a β-jelly roll structure.

@@ Line 29: / Line 29: @@
 == Substrate specificities ==
-The family GH17 glycoside hydrolases are clan GH-A enzymes from bacteria, fungi and plants, and include two major groups of enzymes with related but distinct substrate specificities, namely 1,3-β-D-glucan endohydrolases ([{{EClink}}3.2.1.39 EC 3.2.1.39]) and 1,3;1,4-β-D-glucan endohydrolases ([{{EClink}}3.2.1.73 EC 3.1.2.73]).  A 1,3-β-D-glucan exohydrolase ([{{EClink}}3.2.1.58 EC 3.1.2.58]) is also classified in this family.  The family GH17 enzymes have quite distinct amino acid sequences and 3D structures compared with the 1,3-β-D-glucan endohydrolases and 1,3;1,4-β-D-glucan endohydrolases that have similar substrate specificities but are classified in families [[GH16]], [[GH55]], GH64 and GH81.
+The family GH17 [[glycoside hydrolase]]s are clan GH-A enzymes from bacteria, fungi and plants, and include two major groups of enzymes with related but distinct substrate specificities, namely 1,3-β-D-glucan [[endo]]hydrolases ([{{EClink}}3.2.1.39 EC 3.2.1.39]) and 1,3;1,4-β-D-glucan endohydrolases ([{{EClink}}3.2.1.73 EC 3.1.2.73]).  A 1,3-β-D-glucan exohydrolase ([{{EClink}}3.2.1.58 EC 3.1.2.58]) is also classified in this family.  The family GH17 enzymes have quite distinct amino acid sequences and 3D structures compared with the 1,3-β-D-glucan endohydrolases and 1,3;1,4-β-D-glucan [[endo]]hydrolases that have similar substrate specificities but are classified in families [[GH16]], [[GH55]], GH64 and GH81.
-The family GH17 1,3-β-D-glucan endohydrolases hydrolyse internal 1,3-β-D-glucosidic linkages in polysaccharides, but usually require a region of contiguous unbranched, un-substituted 1,3-β-D-glucosyl residues for activity.  The enzymes release 1,3-β-D-oligoglucosides of DP 2-5 as their major products. Because the 1,3-β-D-glucan endohydrolases require a region of contiguous unbranched, un-substituted 1,3-β-D-glucosyl residues for activity, they are unable to hydrolyse the single 1,3-β-D-glucosidic linkages in 1,3;1,4-β-D-glucans from the Poaceae, but they will hydrolyse  1,3-β-D-glucosidic linkages in fungal 1,3;1,6-β-D-glucans, provided an appropriate region of contiguous un-substituted 1,3-β-D-glucosyl residues is available. The family GH17 1,3;1,4-β-D-glucan endohydrolases ([{{EClink}}3.2.1.73 EC 3.1.2.73]) hydrolyse 1,4-β-D-glucosidic linkages, but only 1,3;1,4-β-D-glucans in which the glucosyl residue involved in the glycosidic linkage cleaved is substituted at the C(0)3 position, that is, where the 1,4-β-D-glucosidic linkages are located on the reducing end side of 1,3-β-D-glucosyl residues.
+The family GH17 1,3-β-D-glucan [[endo]]hydrolases hydrolyse internal 1,3-β-D-glucosidic linkages in polysaccharides, but usually require a region of contiguous unbranched, un-substituted 1,3-β-D-glucosyl residues for activity.  The enzymes release 1,3-β-D-oligoglucosides of DP 2-5 as their major products. Because the 1,3-β-D-glucan endohydrolases require a region of contiguous unbranched, un-substituted 1,3-β-D-glucosyl residues for activity, they are unable to hydrolyse the single 1,3-β-D-glucosidic linkages in 1,3;1,4-β-D-glucans from the Poaceae, but they will hydrolyse  1,3-β-D-glucosidic linkages in fungal 1,3;1,6-β-D-glucans, provided an appropriate region of contiguous un-substituted 1,3-β-D-glucosyl residues is available. The family GH17 1,3;1,4-β-D-glucan endohydrolases ([{{EClink}}3.2.1.73 EC 3.1.2.73]) hydrolyse 1,4-β-D-glucosidic linkages, but only 1,3;1,4-β-D-glucans in which the glucosyl residue involved in the glycosidic linkage cleaved is substituted at the C(0)3 position, that is, where the 1,4-β-D-glucosidic linkages are located on the reducing end side of 1,3-β-D-glucosyl residues.
 Reaction products released are mainly 1,3;1,4-β-D-tri- and tetrasaccharides (G4G3G<sub>red</sub> and G4G4G3G<sub>red</sub>), but they also release higher oligosaccharides of up to 10 or more contiguous 1,4-β-D-glucosyl residues with a single reducing terminal 1,3-β-D-glucosyl residue (e.g. G4G4G4G4G4G4G3G<sub>red</sub>).  These longer oligosaccharides originate from the longer regions of adjacent 1,4-linkages that account for approximately 10% by weight of 1,3;1,4-β-D-glucans in cell walls of the [http://en.wikipedia.org/wiki/Poaceae Poaceae] <cite>Woodward</cite>.
 == Kinetics and Mechanism ==
-The stereochemistry of the reaction has been determined experimentally and catalysis by GH17 enzymes occurs via a double displacement mechanism and the β-anomeric configuration of the released oligosaccharide is retained <cite>Chen1995</cite>.  Detailed kinetic analyses are available for three purified barley 1,3-β-D-glucan endohydrolases and two barley 1,3;1,4-β-D-glucan endohydrolases <cite>Chen1995</cite>.
+The stereochemistry of the reaction has been determined experimentally and catalysis by GH17 enzymes occurs via a [[classical Koshland retaining mechanism]] with the β-anomeric configuration of the released oligosaccharide being retained <cite>Chen1995</cite>.  Detailed kinetic analyses are available for three purified barley 1,3-β-D-glucan endohydrolases and two barley 1,3;1,4-β-D-glucan endohydrolases <cite>Chen1995</cite>.
 == Catalytic Residues ==
-Active site labelling with epoxyalkyl-β-D-oligoglucoside inhibitors identified Glu231 and Glu232 as the catalytic nucleophiles of the barley 1,3- and 1,3;1,4-β-D-glucan endohydrolases, respectively <cite>Chen1993</cite>, located at the bottom of, and about two-thirds of the way along the substrate binding cleft.  The catalytic acid/base residue of 1,3;1,4-β-D-glucan endohydrolase was initially identified as Glu288 by chemical labelling procedures <cite>Chen1993 Chen1995b</cite>, but this assignment was subsequently revised and Glu93 was proposed based on primary and tertiary structure similarity of GH17 enzymes with clan GH-A β-glycosidases <cite>Jenkins1998 Henrissat</cite>. The 5-6 Å distance between Glu232 and Glu93 is typical of retaining enzymes.
+Active site labelling with epoxyalkyl-β-D-oligoglucoside inhibitors identified Glu231 and Glu232 as the [[catalytic nucleophile]]s of the barley 1,3- and 1,3;1,4-β-D-glucan endohydrolases, respectively <cite>Chen1993</cite>, located at the bottom of, and about two-thirds of the way along the substrate binding cleft.  The [[general acid/base]] residue of 1,3;1,4-β-D-glucan endohydrolase was initially identified as Glu288 by chemical labelling procedures <cite>Chen1993 Chen1995b</cite>, but this assignment was subsequently revised and Glu93 was proposed based on primary and tertiary structure similarity of GH17 enzymes with clan GH-A β-glycosidases <cite>Jenkins1998 Henrissat</cite>. The 5-6 Å distance between Glu232 and Glu93 is typical of retaining enzymes.
 == Three-dimensional structures ==
@@ Line 51: / Line 51: @@
 == Family Firsts ==
 ;First sterochemistry determination:  The stereochemical course of hydrolysis of ''Laminaria digitata'' laminarin and barley 1,3;1,4-β-glucan by barley 1,3-β-glucanase isoenzyme GII and 1,3;1,4-β-glucanase isoenzyme EII, respectively, was determined by <sup>1</sup>H-NMR. Both enzymes catalyze hydrolysis with retention of anomeric configuration (e-->e) and may therefore operate via a double displacement mechanism <cite>Chen1995</cite>.
-;First catalytic nucleophile identification: Active site labelling with epoxyalkyl-β-D-oligoglucoside inhibitors identified Glu231 and Glu232 as the catalytic nucleophiles of the barley 1,3- and 1,3;1,4-β-D-glucan endohydrolases, respectively <cite>Chen1993</cite>.
+;First [[catalytic nucleophile]] identification: Active site labelling with epoxyalkyl-β-D-oligoglucoside inhibitors identified Glu231 and Glu232 as the catalytic nucleophiles of the barley 1,3- and 1,3;1,4-β-D-glucan endohydrolases, respectively <cite>Chen1993</cite>.
-;First general acid/base residue identification: This residue was identified as the conserved Glu residue at the C-terminal end of strand β-4 based on primary and tertiary structure similarity of GH17 enzymes with clan GH-A β-glycosidases <cite>Jenkins1998 Henrissat</cite>.
+;First [[general acid/base]] residue identification: This residue was identified as the conserved Glu residue at the C-terminal end of strand β-4 based on primary and tertiary structure similarity of GH17 enzymes with clan GH-A β-glycosidases <cite>Jenkins1998 Henrissat</cite>.
 ;First 3-D structure: Barley 1,3-β-D-glucan endohydrolase isoenzyme GII and 1,3;1,4-β-D-glucan endohydrolase isoenzyme EII, solved to 2.2-2.3 Å resolution <cite>Varghese</cite>.

@@ Line 53: / Line 53: @@
 ;First catalytic nucleophile identification: Active site labelling with epoxyalkyl-β-D-oligoglucoside inhibitors identified Glu231 and Glu232 as the catalytic nucleophiles of the barley 1,3- and 1,3;1,4-β-D-glucan endohydrolases, respectively <cite>Chen1993</cite>.
 ;First general acid/base residue identification: This residue was identified as the conserved Glu residue at the C-terminal end of strand β-4 based on primary and tertiary structure similarity of GH17 enzymes with clan GH-A β-glycosidases <cite>Jenkins1998 Henrissat</cite>.
-;First 3-D structure: Cite some reference here, with a ''short'' (1-2 sentence) explanation <cite>Varghese</cite>.
+;First 3-D structure: barley 1,3-β-D-glucan endohydrolase isoenzyme GII and 1,3;1,4-β-D-glucan endohydrolase isoenzyme EII, solved to 2.2-2.3 Å resolution <cite>Varghese</cite>.
 == References ==