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Glycoside Hydrolase Family 93

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Glycoside Hydrolase Family GH93
Clan GH-E
Mechanism retaining
Active site residues known
CAZy DB link
http://www.cazy.org/fam/GH93.html

Substrate specificities

The characterized member of family 93 are known to hydrolyse α-1,5-L-arabinan. EC:3.2.1-

Kinetics and Mechanism

GH93 enzymes are exoenzymes which only release arabinobiose from the non-reducing end. Net retention of the configuration of the anomeric carbon is proposed from the products of the transglycosylation activity of the protein Abnx from Penicillium chrysogenum. It was recently supported in the crystal structure of the Arb93A enzyme from Fusarium graminearum in complex with arabinobiose.

Catalytic Residues

From the crystal structure of Arb93A, Glu170 and Glu242 are proposed to act as nucleophile and acid/base respectively. Mutagenesis experiment support their role in catalysis and they are strictly conserved between the family members.

Three-dimensional structures

The recent crystal structure of Arb93A reveals a six-bladed beta-propeller fold characteristic of sialidases of clan GHE. The catalytic machinery is however very different from that of sialidases.

Family Firsts

References