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
http://www.cazy.org/CE20.html

Substrate specificities

Carbohydrate esterase family 20 (CE20) currently comprises xyloglucan acetylesterases (E.C. 3.2.1.6) [1] and acetylesterases putatively related to arabinoxylan deacetylation [2] .

Catalytic Residues

XacXaeA, the founding member of family CE20 [1], harbors the canonical catalytic triad Ser-Asp-His and the conserved oxyanion hole. Thus, it is supposed to have the same mechanism of action described for other carbohydrate esterases, such as the members of family CE3 and CE6. However, this assumption still requires experimental validation. The catalytic-relevant residues are present in consensus regions in Xanthomonas, denoted as Block I (GQSNME) and Block V (DIH). Oxyanion hole residues are present in Blocks I (GQSNME) and III (YQGET). Although consensus Block II is present, Block IV is absent [1], as noted for other related carbohydrate esterase (CE) families.

Kinetics and Mechanism

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, XuaJ, is available for the substrate 1-Naphthyl acetate [2].

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 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.

[[Image:Ce20_cazypedia.png|thumb|300px|Figure 1: Adapted from [1] originally published under Creative Commons Attribution 4.0 International License.

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 biochemical characterization

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

First 3-D structure

Xanthomonas citri subsp. citri 306 xyloglucan acetylesterase crystal structure in 2021 PDB ID 7KMM [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.