Carbohydrate Esterase Family 20

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• Authors: Plinio Salmazo Vieira and Priscila Oliveira Giuseppe
• Responsible Curator: Mario Murakami

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Carbohydrate Esterase Family CE20
Fold	β-sandwich/(α-β-α) sandwich/β-sandwich
Mechanism	serine hydrolase
Active site residues	known
CAZy DB link
https://www.cazy.org/CE20.html

Substrate specificities

Carbohydrate esterase family 20 (CE20) currently comprises xyloglucan acetylesterases [1] and acetylesterases putatively related to arabinoxylan deacetylation [2] .

Kinetics and Mechanism

XacXaeA, the founding member of family CE20 [1], harbors the canonical catalytic triad (Asp-His-Ser). Thus, it is supposed to have the same mechanism of action described for other carbohydrate esterases, such as the members of family CE1. However, this assumption still requires experimental validation. XacXaeA is specific to O-acetylation since it is not capable of cleaving N-acetylated carbohydrates. It shows activity on a broad range of O-acetylated mono- and disaccharides and did not show a positional preference for acetylated oxygens. XacXaeA was active towards cell wall extracted xyloglucan oligosaccharides, deacetylating distinct types of structures such as XXLG/XLXG, XXFG, and XLFG [1]. Kinetic data for the second characterized member of family CE20 is available for the substrate 1-Naphthyl acetate [2].

Catalytic Residues

The founding members of this family seem to have the canonical catalytic triad (Asp-His-Ser) found in esterases from other families [1], but this inference still requires experimental validation.

Three-dimensional structures

The CE20 structure is composed of a central catalytic core, which displays the SGNH hydrolase fold, flanked by two antiparallel seven-stranded β-sandwiches intimately linked to the central core, forming a monolithic structure [1]. Such structural architecture diverges from carbohydrate esterase (CE) families described in the CAZy database so far. In XacXaeA, the founding member of family CE20 [1], the catalytic core is composed of two halves (residues 104-216 and 397-541) due to the insertion of a domain (residues 217-396, named X448 in the CAZy database [3, 4]) in the α5-η3 loop .

Family Firsts

First stereochemistry determination

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First catalytic nucleophile identification

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First general acid/base residue identification

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First 3-D structure

Xanthomonas citri subsp. citri 306 xyloglucan acetylesterase crystal structure in 2021 [1].

References

1. Vieira PS, Bonfim IM, Araujo EA, Melo RR, Lima AR, Fessel MR, Paixão DAA, Persinoti GF, Rocco SA, Lima TB, Pirolla RAS, Morais MAB, Correa JBL, Zanphorlin LM, Diogo JA, Lima EA, Grandis A, Buckeridge MS, Gozzo FC, Benedetti CE, Polikarpov I, Giuseppe PO, and Murakami MT. (2021). Xyloglucan processing machinery in Xanthomonas pathogens and its role in the transcriptional activation of virulence factors. Nat Commun. 2021;12(1):4049. DOI:10.1038/s41467-021-24277-4 |
2. Liu N, Gagnot S, Denis Y, Byrne D, Faulds C, Fierobe HP, and Perret S. (2022). Selfish uptake versus extracellular arabinoxylan degradation in the primary degrader Ruminiclostridium cellulolyticum, a new string to its bow. Biotechnol Biofuels Bioprod. 2022;15(1):127. DOI:10.1186/s13068-022-02225-8 |
3. Cantarel BL, Coutinho PM, Rancurel C, Bernard T, Lombard V, and Henrissat B. (2009). The Carbohydrate-Active EnZymes database (CAZy): an expert resource for Glycogenomics. Nucleic Acids Res. 2009;37(Database issue):D233-8. DOI:10.1093/nar/gkn663 |

4. Davies, G.J. and Sinnott, M.L. (2008) Sorting the diverse: the sequence-based classifications of carbohydrate-active enzymes. The Biochemist, vol. 30, no. 4., pp. 26-32. Download PDF version.