Glycoside Hydrolase Family 141

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• Author: ^^^Ana Luis^^^
• Responsible Curator: ^^^Harry Gilbert^^^

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Glycoside Hydrolase Family GH141
Clan	none
Mechanism	unknown
Active site residues	known
CAZy DB link
https://www.cazy.org/GH141.html

Substrate specificities

Glycoside hydrolases of family 141 (CAZy) display α-L-fucosidase (EC 3.2.1.51) [1] or xylanase (EC 3.2.1.8) [2]activities. The Bacteroides thetaiotaomicron enzyme BT1002 was the founding member of this family. The enzyme cleaves the fucosodic linkage in 2-O-methyl-D-xylose-α-1,3-L-fucose-α1,4-L-Rhap, a component of Chain B of rhamnogalacturonan II, a complex pectin conserved in the primary cell walls [1]. Recently, an endo-xylanase from Clostridium thermocellum (Xyn141E) was also described. Xyn141E is active against a range of xylans, displaying lowl elvel side activity against other β1,4-glycans such as carboxymethyl cellulose, barley beta glucan and mannan from ivory nut [2].

Kinetics and Mechanism

Very little is known about the kinetics or mechanism of GH141 enzymes. However, in the BT1002 crystal structure, the distance of 6.1 Å between the catalytic residues suggests that members of this family may be retaining enzymes and follow a double displacement mechanism [1].

Catalytic Residues

In the BT1002 crystal structure, two aspartates (Asp523 and Asp564), which are highly conserved and located within the active site pocket, are the proposed catalytic residues. Site directed mutagenesis of these amino acids abolished the catalytic activity of BT1002 indicating the essential role in catalysis. Additionally, the structural location of the catalytic residues suggests that Asp523 (at the base of the pocket) acts as catalytic nucleophile and Asp564 (at the lip of the active site) is the general acid-base residue [1].

Three-dimensional structures

Figure 1. BT1002 strucutre. (PDB ID 5PDB) The figure shows the β-parallel catalytic domain (purple) and the additional β-sandwich domain (yellow)

The three-dimensional structure has been solved for B. thetaiotaomicron BT1002 at 2 Å (PDB ID 5PDB). The protein has two domains: a N-terminal β-sandwich and a C-terminal β-parallel helical catalytic domain (Figure 1) [1]. The active site pocket is in a similar location to the catalytic centre of GH120 β-xylosidases

Family Firsts

First stereochemistry determination

Currently unknown.

First catalytic nucleophile identification

BT1002 from Bacteroides thetaiotaomicron [1].

First general acid/base residue identification

BT1002 from Bacteroides thetaiotaomicron [1].

First 3-D structure

BT1002 from Bacteroides thetaiotaomicron [1].

References

1. Ndeh D, Rogowski A, Cartmell A, Luis AS, Baslé A, Gray J, Venditto I, Briggs J, Zhang X, Labourel A, Terrapon N, Buffetto F, Nepogodiev S, Xiao Y, Field RA, Zhu Y, O'Neil MA, Urbanowicz BR, York WS, Davies GJ, Abbott DW, Ralet MC, Martens EC, Henrissat B, and Gilbert HJ. (2017). Complex pectin metabolism by gut bacteria reveals novel catalytic functions. Nature. 2017;544(7648):65-70. DOI:10.1038/nature21725 |
2. Heinze S, Mechelke M, Kornberger P, Liebl W, Schwarz WH, and Zverlov VV. (2017). Identification of endoxylanase XynE from Clostridium thermocellum as the first xylanase of glycoside hydrolase family GH141. Sci Rep. 2017;7(1):11178. DOI:10.1038/s41598-017-11598-y |