Glycoside Hydrolase Family 7

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• Author: ^^^Jerry Stahlberg^^^
• Responsible Curator: ^^^Jerry Stahlberg^^^

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Glycoside Hydrolase Family 7
Clan	GH-B
Mechanism	retaining
Active site residues	known
CAZy DB link
http://www.cazy.org/fam/GH7.html

Substrate specificities

Most glycoside hydrolases of family 7 cleave β-1,4 glycosidic bonds in cellulose/β-1,4-glucans. Several members also show activity on xylan. The substrate specificities found in GH7 are: endo-1,4-β-glucanase (EC 3.2.1.4), [reducing end-acting] cellobiohydrolase (EC 3.2.1.-), chitosanase (EC 3.2.1.132) and endo-1,3-1,4-β-glucanase (EC 3.2.1.73).

Kinetics and Mechanism

Family 7 enzymes are retaining enzymes, as first shown by NMR [1] on Cellobiohydrolase I (CBH I; Cel7A) from the fungus Trichoderma reesei (a clonal derivative of Hypocrea jecorina [2]).

Catalytic Residues

In GH7 enzymes the catalytic residues are positioned close to each other in sequence in the consensus motif -Glu-X-Asp-X-X-Glu-, where the first Glu acts as catalytic nucleophile and the other Glu as general acid/base. This was proposed in the first 3-D structure publication, of H. jecorina Cel7A [3], based on the position of the residues relative to a o-iodo-benzyl-cellobioside molecule bound at the active site. It was supported by mutational studies with the same enzyme [4], which also showed that the Aspartate residue in the consensus motif is important for catalysis, and with Endoglucanase I (EG I, Cel7B) from Humicola insolens [5]. The catalytic nucleophile was further supported by affinity labelling with 3,4-epoxybutyl-β-cellobioside; with H. jecorina Cel7A the identification was done by ESI-MS peptide mapping and sequencing [6], and with Fusarium oxysporum Endoglucanase I (EG I, Cel7B) the residue was identified by X-ray crystallography [7]. This was subsequently verified by trapping of a 2-deoxy-2-fluorocellotriosyl covalent enzyme intermediate and identification of the labelled peptide by tandem MS [5].

Three-dimensional structures

Content is to be added here.

Family Firsts

First sterochemistry determination

Hypocrea jecorina cellobiohydrolase Cel7A by NMR [1].

First catalytic nucleophile identification

Cite some reference here, with a short (1-2 sentence) explanation [8].

First general acid/base residue identification

Cite some reference here, with a short (1-2 sentence) explanation [9].

First 3-D structure

First cellobiohydrolase was Hypocrea jecorina Cel7A (CBH I; PDB 1cel) [3]. First endo-1,4-β-glucanase was Endoglucanase I (EG I, Cel7B) from Fusarium oxysporum (PDB 1ovw) [10], both by X-ray crystallography.

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. Divne C, Ståhlberg J, Reinikainen T, Ruohonen L, Pettersson G, Knowles JK, Teeri TT, and Jones TA. (1994). The three-dimensional crystal structure of the catalytic core of cellobiohydrolase I from Trichoderma reesei. Science. 1994;265(5171):524-8. DOI:10.1126/science.8036495 |
4. Ståhlberg J, Divne C, Koivula A, Piens K, Claeyssens M, Teeri TT, and Jones TA. (1996). Activity studies and crystal structures of catalytically deficient mutants of cellobiohydrolase I from Trichoderma reesei. J Mol Biol. 1996;264(2):337-49. DOI:10.1006/jmbi.1996.0644 |
5. MacKenzie LF, Sulzenbacher G, Divne C, Jones TA, Wöldike HF, Schülein M, Withers SG, and Davies GJ. (1998). Crystal structure of the family 7 endoglucanase I (Cel7B) from Humicola insolens at 2.2 A resolution and identification of the catalytic nucleophile by trapping of the covalent glycosyl-enzyme intermediate. Biochem J. 1998;335 ( Pt 2)(Pt 2):409-16. DOI:10.1042/bj3350409 |
6. Klarskov K, Piens K, Ståhlberg J, Høj PB, Beeumen JV, and Claeyssens M. (1997). Cellobiohydrolase I from Trichoderma reesei: identification of an active-site nucleophile and additional information on sequence including the glycosylation pattern of the core protein. Carbohydr Res. 1997;304(2):143-54. DOI:10.1016/s0008-6215(97)00215-2 |
7. Sulzenbacher G, Schülein M, and Davies GJ. (1997). Structure of the endoglucanase I from Fusarium oxysporum: native, cellobiose, and 3,4-epoxybutyl beta-D-cellobioside-inhibited forms, at 2.3 A resolution. Biochemistry. 1997;36(19):5902-11. DOI:10.1021/bi962963+ |

8. Sinnott, M.L. (1990) Catalytic mechanisms of enzymic glycosyl transfer. Chem. Rev. 90, 1171-1202. DOI: 10.1021/cr00105a006

9. He S and Withers SG. (1997). Assignment of sweet almond beta-glucosidase as a family 1 glycosidase and identification of its active site nucleophile. J Biol Chem. 1997;272(40):24864-7. DOI:10.1074/jbc.272.40.24864 |
10. Sulzenbacher G, Driguez H, Henrissat B, Schülein M, and Davies GJ. (1996). Structure of the Fusarium oxysporum endoglucanase I with a nonhydrolyzable substrate analogue: substrate distortion gives rise to the preferred axial orientation for the leaving group. Biochemistry. 1996;35(48):15280-7. DOI:10.1021/bi961946h |
11. Robert V. Stick and Spencer J. Williams. (2009) Carbohydrates. Elsevier Science.