| 词条 | Glycoside hydrolase family 20 |
| 释义 |
| Symbol = Glyco_hydro_20 | Name = Glycosyl hydrolase family 20, catalytic domain | image = PDB 1m01 EBI.jpg | width = | caption = wildtype streptomyces plicatus beta-hexosaminidase in complex with product (glcnac) | Pfam = PF00728 | Pfam_clan = CL0058 | InterPro = IPR015883 | SMART = | PROSITE = | MEROPS = | SCOP = 1qba | TCDB = | OPM family = | OPM protein = | CAZy = GH20 | CDD = cd02742 }}{{Infobox protein family | Symbol = Glyco_hydro_20b | Name = Glycosyl hydrolase family 20, domain 2 | image = PDB 2gjx EBI.jpg | width = | caption = crystallographic structure of human beta-hexosaminidase a | Pfam = PF02838 | Pfam_clan = | InterPro = IPR015882 | SMART = | PROSITE = | MEROPS = | SCOP = 1qba | TCDB = | OPM family = | OPM protein = | CAZy = GH20 | CDD = }} In molecular biology, glycoside hydrolase family 20 is a family of glycoside hydrolases. Glycoside hydrolases {{EC number|3.2.1.}} are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycoside hydrolases, based on sequence similarity, has led to the definition of >100 different families.[1][2][3] This classification is available on the CAZy web site,[4][5] and also discussed at CAZypedia, an online encyclopedia of carbohydrate active enzymes.[6][7]Glycoside hydrolase family 20 CAZY GH_20 comprises enzymes with several known activities; beta-hexosaminidase ({{EC number|3.2.1.52}}); lacto-N-biosidase ({{EC number|3.2.1.140}}). Carbonyl oxygen of the C-2 acetamido group of the substrate acts as the catalytic nucleophile/base in this family of enzymes. In the brain and other tissues, beta-hexosaminidase A degrades GM2 gangliosides; specifically, the enzyme hydrolyses terminal non-reducing N-acetyl-D-hexosamine residues in N-acetyl-beta-D-hexosaminides. There are 3 forms of beta-hexosaminidase: hexosaminidase A is a trimer, with one alpha, one beta-A and one beta-B chain; hexosaminidase B is a tetramer of two beta-A and two beta-B chains; and hexosaminidase S is a homodimer of alpha chains. The two beta chains are derived from the cleavage of a precursor. Mutations in the beta-chain lead to Sandhoff disease, a lysosomal storage disorder characterised by accumulation of GM2 ganglioside.[8] References1. ^{{cite journal | vauthors = Henrissat B, Callebaut I, Fabrega S, Lehn P, Mornon JP, Davies G | title = Conserved catalytic machinery and the prediction of a common fold for several families of glycosyl hydrolases | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 92 | issue = 15 | pages = 7090–4 | date = July 1995 | pmid = 7624375 | pmc = 41477 | doi = 10.1073/pnas.92.15.7090 }} {{InterPro content|IPR015883}}{{Sugar hydrolases}}{{Enzymes}}{{Portal bar|Molecular and Cellular Biology|border=no}}2. ^{{cite journal | vauthors = Davies G, Henrissat B | title = Structures and mechanisms of glycosyl hydrolases | journal = Structure | volume = 3 | issue = 9 | pages = 853–9 | date = September 1995 | pmid = 8535779 | doi = 10.1016/S0969-2126(01)00220-9 }} 3. ^{{cite journal | vauthors = Henrissat B, Bairoch A | title = Updating the sequence-based classification of glycosyl hydrolases | journal = The Biochemical Journal | volume = 316 ( Pt 2) | issue = Pt 2 | pages = 695–6 | date = June 1996 | pmid = 8687420 | pmc = 1217404 }} 4. ^{{Cite web|url=http://www.cazy.org/|title=Home|last=|first=|date=|website=CAZy.org|language=en|archive-url=|archive-date=|dead-url=|access-date=2018-03-06}} 5. ^{{cite journal | vauthors = Lombard V, Golaconda Ramulu H, Drula E, Coutinho PM, Henrissat B | title = The carbohydrate-active enzymes database (CAZy) in 2013 | journal = Nucleic Acids Research | volume = 42 | issue = Database issue | pages = D490–5 | date = January 2014 | pmid = 24270786 | doi = 10.1093/nar/gkt1178 | url = https://academic.oup.com/nar/article/42/D1/D490/1057423 }} 6. ^{{Cite web|url=http://www.cazypedia.org/index.php/Glycoside_Hydrolase_Family_20|title=Glycoside Hydrolase Family 20|last=|first=|date=|website=CAZypedia.org|language=en|archive-url=|archive-date=|dead-url=|access-date=2018-03-06}} 7. ^{{cite journal | vauthors = | title = Ten years of CAZypedia: a living encyclopedia of carbohydrate-active enzymes | journal = Glycobiology | volume = 28 | issue = 1 | pages = 3–8 | date = December 2018 | pmid = 29040563 | doi = 10.1093/glycob/cwx089 }} 8. ^{{cite journal | vauthors = Bolhuis PA, Ponne NJ, Bikker H, Baas F, Vianney de Jong JM | title = Molecular basis of an adult form of Sandhoff disease: substitution of glutamine for arginine at position 505 of the beta-chain of beta-hexosaminidase results in a labile enzyme | journal = Biochimica et Biophysica Acta | volume = 1182 | issue = 2 | pages = 142–6 | date = September 1993 | pmid = 8357844 | doi = 10.1016/0925-4439(93)90134-m }} 3 : EC 3.2.1|GH family|Protein families |
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