Glycoside Hydrolase Family 6

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• Author: ^^^Kathleen Piens^^^ and ^^^Gideon Davies^^^
• Responsible Curator: ^^^Gideon Davies^^^

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Glycoside Hydrolase Family GH6
Clan	none
Mechanism	inverting
Active site residues	acid known, base debated
CAZy DB link
http://www.cazy.org/fam/GH6.html

Substrate specificities

Glycoside hydrolases of family 6 cleave β-1,4 glycosidic bonds in cellulose/β-1,4-glucans. Only endoglucanase (EC 3.2.1.4) and cellobiohydrolase (EC 3.2.1.91) activity has been reported for both bacterial and eukaryotic members of this family.

Kinetics and Mechanism

Family 6 enzymes are inverting enzymes, as first shown by NMR [1] on Cellobiohydrolase II (CBH II; Cel6A) from the fungus Trichoderma reesei (a clonal derivative of Hypocrea jecorina [2]).

Catalytic Residues

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Table. Putative catalytic residues of some representatives in GH family 6
(with biochemical characterization of wt and mutant enzymes).

Proposed role	CfCel6A (endo)	HiCel6A (exo)	HjCel6A (exo)	TfCel6A (endo)	TfCel6B (exo)
Substrate distortion	Tyr210	Tyr174	Tyr169	Tyr73	Tyr220
Increase in pKa acid/Catalytic base	Asp216	Asp180	Asp175	Asp79	Asp226
Proton network	Gly222?	Ser186	Ser181	Ser85	Ser232
Catalytic acid	Asp252	Asp226	Asp221	Asp117	Asp274
Catalytic base/substrate binding	Asp392	Asp405	Asp401	Asp265	Asp497

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Three-dimensional structures

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Family Firsts

First sterochemistry determination

Hypocrea jecorina cellobiohydrolase Cel6A by NMR [1].

First general acid/base residue identification

Cite some reference here, with a short (1-2 senetence) explanation.

First 3-D structure

The catalytic core domain of the Trichoderma reesei (the organism now known as Hypocrea jecorina) cellobiohydrolase II by the Jones group [3]. The first endoglucanase in this family was the Thermomonospora fusca E2 enzyme (catalytic core) solved by the Wilson/Karplus groups[4]

References

1. Knowles, J.K.C., Lehtovaara, P., Murray, M. and Sinnott, M.L. (1988) Stereochemical course of the action of the cellobioside hydrolases I and II of Trichoderma reesei. J. Chem. Soc., Chem. Commun., 1988, 1401-1402. DOI: 10.1039/C39880001401

2. Kuhls K, Lieckfeldt E, Samuels GJ, Kovacs W, Meyer W, Petrini O, Gams W, Börner T, and Kubicek CP. (1996). Molecular evidence that the asexual industrial fungus Trichoderma reesei is a clonal derivative of the ascomycete Hypocrea jecorina. Proc Natl Acad Sci U S A. 1996;93(15):7755-60. DOI:10.1073/pnas.93.15.7755 |
3. Rouvinen J, Bergfors T, Teeri T, Knowles JK, and Jones TA. (1990). Three-dimensional structure of cellobiohydrolase II from Trichoderma reesei. Science. 1990;249(4967):380-6. DOI:10.1126/science.2377893 |
4. Spezio M, Wilson DB, and Karplus PA. (1993). Crystal structure of the catalytic domain of a thermophilic endocellulase. Biochemistry. 1993;32(38):9906-16. DOI:10.1021/bi00089a006 |