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Glycoside Hydrolase Family 138

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Glycoside Hydrolase Family GH138
Clan none
Mechanism unknown
Active site residues unknown
CAZy DB link

Substrate specificities

Glycoside hydrolases of family 138 exhibit α-D-galacturonidase activity. This is based on data from the characterisation of the founding member of the family BT0997 encoded by the human gut bacterium B. thetaiotaomicron [1]. BT0997 hydrolyses a fragment (GalA-α1,2(GalA-β1,3)(2MeXyl-α1,3-Fuc-α1,4)Rha-α1,3-Api) of chain A from the pectic polysaccharide rhamnogalacturonan II, producing D-galacturonic acid and the resulting oligosaccharide GalA-β1,3(2MeXyl-α1,3Fuc-α1,4)Rha-α1,3Api [1]. Several members of this family have been identified in gut and environmental bacteria with a majority of the encoding microbes belonging to the Bacteroidetes phylum [2, 3]. This phylum is highly represented in human gut microbial populations [4].

Kinetics and Mechanism

The kinetic mechanism for this family has not been reported.

Catalytic Residues

The catalytic residues for this family have not yet been identified.

Three-dimensional structures

No 3D structure for a member of this family has been currently reported.

Family Firsts

First stereochemistry determination
Currently unknown.
First catalytic nucleophile identification
Currently unknown.
First general acid/base residue identification
Currently unknown.
First 3-D structure
Currently unknown.


  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 | PubMed ID:28329766 [Ndeh2017]
  2. Lombard V, Golaconda Ramulu H, Drula E, Coutinho PM, and Henrissat B. (2014). The carbohydrate-active enzymes database (CAZy) in 2013. Nucleic Acids Res. 2014;42(Database issue):D490-5. DOI:10.1093/nar/gkt1178 | PubMed ID:24270786 [Lombard2014]
  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 | PubMed ID:18838391 [Cantarel2009]
  4. Qin J, Li R, Raes J, Arumugam M, Burgdorf KS, Manichanh C, Nielsen T, Pons N, Levenez F, Yamada T, Mende DR, Li J, Xu J, Li S, Li D, Cao J, Wang B, Liang H, Zheng H, Xie Y, Tap J, Lepage P, Bertalan M, Batto JM, Hansen T, Le Paslier D, Linneberg A, Nielsen HB, Pelletier E, Renault P, Sicheritz-Ponten T, Turner K, Zhu H, Yu C, Li S, Jian M, Zhou Y, Li Y, Zhang X, Li S, Qin N, Yang H, Wang J, Brunak S, Doré J, Guarner F, Kristiansen K, Pedersen O, Parkhill J, Weissenbach J, MetaHIT Consortium, Bork P, Ehrlich SD, and Wang J. (2010). A human gut microbial gene catalogue established by metagenomic sequencing. Nature. 2010;464(7285):59-65. DOI:10.1038/nature08821 | PubMed ID:20203603 [Qin2010]

All Medline abstracts: PubMed